|tyler8611||5/29/2018 7:05 PM|
|Deluxe Reverb problem|
Hi, I've built a deluxe reverb clone and have hit a snag. My screen and plate voltages on the 6v6s are both only 153v. I get a zero reading on pin 8 (through 1 ohm resistors), both mA and mV. I measured and set the negative bias voltage at -35. It's not a tube problem- already swapped another pair with same results.
B+ is 440, then the second node drops all the way down to the 153v. The remaining power caps measure about as they should.
Obviously there's no output, unless I dime channel 1 and get faint crackling notes. Vibrato channel is silent all the way up.
Does this seem like a power cap or maybe transformer problem? I've checked the wiring and solder joints thoroughly.
|Leo_Gnardo||5/29/2018 7:14 PM|
Also possible the hi voltage nodes are wired in an out-of-order way.
|The Dude||5/29/2018 7:23 PM|
|I'm confused. You say, "B+ is 440". Then you say, "My screen and plate voltages on the 6v6s are both only 153v" The output tube plate node (B+) is before the choke and goes through the OT directly to the plates. You almost have to have something wired wrong.|
|tyler8611||5/29/2018 7:25 PM|
|tyler8611||5/29/2018 7:28 PM|
|tyler8611||5/29/2018 7:33 PM|
|The Dude||5/29/2018 7:35 PM|
|Yes. I understand. If you look at "pin 8 of the rectifier to the first power cap node", follow it up through the OT. It connects directly to the tube plates. If you measure 440VDC there, you should also measure it on the plates, unless you have a horribly bad, hot, melted standby switch. Measure DC on both sides of the standby switch. Is it the same on both with the switch closed?|
|tyler8611||5/29/2018 7:36 PM|
|tyler8611||5/29/2018 7:43 PM|
|Leo_Gnardo||5/29/2018 8:02 PM|
|The Dude||5/29/2018 8:11 PM|
|IMO, the problem is before the choke. According to post #1 the plate voltage is also low. The plate voltage is derived "pre-choke". I'd like to know if the same DCV exists on both sides of the standby switch. Then, if we're good there, we see what the voltage is on the OT primary CT. It should be easy to follow the voltage and see where it's not. The B+ caps should be the same electrical point as the plates as far as DC is concerned, yet we have 2 different voltage readings, so I agree- something is not connected properly.|
|galaxiex||5/29/2018 9:17 PM|
|Don't know if this is your problem, but I replaced the filter caps in the dog house on my 78 SFDR.|
When I powered up, something was not right, I never measured any voltages and nothing smoked... but I knew something was "off".
Powered down and checked my work... one of the cap leads I soldered into the eyelet was a bit long, and it missed the insulating card and shorted to the chassis.
Maybe have a look in that area.
|tyler8611||5/29/2018 10:15 PM|
I also measured the resistance of the transformer and choke leads and they were fine. I drained the filter caps and measured those and the readings began around 90k and kept creeping upwards past 150k, so I'm not sure whether that's normal.
I ran a flashlight under the filter cap board- no shorts. I'll have to keep searching.
|tyler8611||5/29/2018 10:18 PM|
|The Dude||5/29/2018 10:23 PM|
|tyler8611||5/29/2018 10:30 PM|
|The Dude||5/29/2018 10:34 PM|
|Again, please measure the voltage on both sides of the standby switch (switch closed) and tell us what you have. Then, measure the voltage on the center tap of the primary of the output transformer and report.|
|tyler8611||5/29/2018 11:04 PM|
|Enzo||5/29/2018 11:30 PM|
When you check something, please don't tell us it is "fine", please tell us what you measured. We don't know what you consider fine, and we want to know specific values.
You have 440 at the standby switch? OK. What do you have at the OT CT?
To me "second node" is the downhill side of the choke, ie the screens. It bothers me you have the SAME voltage at both plates and screens, even though ther is a choke and transformer between those two places.
What voltages do you get there with power tubes removed?
The standby switch should be on at all times here. ON means closed, the operate position. You should have your 440v on both sides of that switch.
|pdf64||5/30/2018 3:38 AM|
|It may be helpful to note that in a parallel thread on TAG, the OP has revealed a 'trickle bypass' mod to the standby arrangement Deluxe Reverb voltages - Page 2 - The Amp Garage|
Hence standby mode is not as we would normally know it.
Most amps described as clones aren't; it's way better to provide an accurate schematic, rather than provide text descriptions of deviations to an existing design.
|J M Fahey||5/30/2018 4:37 AM|
Quote Originally Posted by The Dude View Post
Yes. I understand. If you look at "pin 8 of the rectifier to the first power cap node", follow it up through the OT. It connects directly to the tube plates. If you measure 440VDC there, you should also measure it on the plates, unless you have a horribly bad, hot, melted standby switch. Measure DC on both sides of the standby switch. Is it the same on both with the switch closed?
"True" is not an answer.
"everything is wired correctly" is obviously not the case.
It may be helpful to note that in a parallel thread on TAG, the OP has revealed a 'trickle bypass' mod to the standby arrangement Deluxe Reverb voltages - Page 2 - The Amp Garage
If so, why didnīt you mention it?
Please post the schematic of said "trickle bypass".
"Standby ON means switch closed, passing current to the OT and power tubes"
"Standby OFF means switch open, NOT passing current to the OT and power tubes"
Nobody knows what trickle Bypass actually means but just from its name it looks like a BAD idea.
|tyler8611||5/30/2018 6:47 AM|
I will check and monitor the mains Vac and provide readings.
|tyler8611||5/30/2018 6:49 AM|
|tyler8611||5/30/2018 7:11 AM|
|I'll be providing exact detailed measurements all at once asap. I appreciate you guys.|
|tyler8611||5/30/2018 7:52 AM|
|tyler8611||5/30/2018 7:55 AM|
|And I can certainly remove the trickle bypass if anyone thinks it's making this more difficult. But like I said, I've always used it. I think it's a sensible, but obviously not mandatory mod.|
|pdf64||5/30/2018 7:59 AM|
Please take a bit of time and review it carefully against your build.
We'll assume that a grounded mains cable and chassis have been used, and the death cap and switch omitted, unless you say otherwise.
I suggest that it is removed from the circuit (at least that will remove terminology confusion), and that you then power up via a light bulb limiter.
|tyler8611||5/30/2018 8:20 AM|
I don't have a light bulb limiter but I probably do have another new switch that I can substitute. I will check my parts bin.
|Leo_Gnardo||5/30/2018 8:59 AM|
This may explain one reason for some of your Deluxe's misbehavior.
Another, if the meaning of "standby" is inverted, and you have a trickle resistor to partially charge the power supply, it would be expected to see 440V one side of the standby switch and some lower voltage say 153 on the other, when the switch is open. When the switch contacts are closed, the same voltage will exist on both switch terminals.
|tyler8611||5/30/2018 9:39 AM|
I hear what you're saying on the standby, but somehow the reverse is happening. Doesn't make sense because the standby wires are going to their proper lugs on the switch. I will have to try a new one.
|Leo_Gnardo||5/30/2018 10:07 AM|
I hear what you're saying on the standby, but somehow the reverse is happening. Doesn't make sense because the standby wires are going to their proper lugs on the switch. I will have to try a new one.
|pdf64||5/30/2018 10:46 AM|
|I think Leo's hunch is right, the zeners may be screwing up the bias supply.|
I suggest to take them out of circuit and review.
I think that a light bulb limiter is second only to a multimeter as being most important resource on a tech's bench.
I suggest to build one before proceeding further.
|g1||5/30/2018 12:44 PM|
|tyler8611||5/30/2018 1:30 PM|
|Fender Power Transformer, Deluxe, Deluxe Reverb, Tweed Tremolux, 125P23B, 025130, 041316, 120V|
And you were right about me stupidly forgetting the direction of the standby switch. Unbelievable. Haven't dealt with blackface amps in a long time. Totally slipped my mind!
Now, the problem is the bias is only 4 mA max. So the zeners may indeed be causing this to happen. Currently, the bias tail resistor is 10k. The range resistor, which I may try changing next, is the standard 470 ohm. I was thinking of upping it to 1.5k, which was the next highest metal oxide resistor I could find.
Then again, maybe I should go ahead and remove the zeners. I'll let you guys chime in.
|tyler8611||5/30/2018 1:32 PM|
|Leo_Gnardo||5/30/2018 2:26 PM|
|tyler8611||5/30/2018 7:03 PM|
|tyler8611||5/30/2018 10:26 PM|
|So I unsoldered and grounded the center tap and left the bias arrangement per schematic. Switched it on (standby open) and while I was at it took a measurement of the B+ coming off the rectifier. It eventually reached 497v, and a few minutes later, exactly 500.|
I took it off standby and it immediately began motorboating and the tubes were glowing blue. They measured 17 mA. I turned the bias pot and there was no change in the reading. I figured that may be bad and have another to replace it.
Last thing I did was measure the B+ and it was 404v. I should have measured everything but I couldn't take the motorboating anymore. So next is change the bias pot and maybe the tail resistor, and if that doesn't work I'll try to see if it's the tubes.
|pdf64||5/31/2018 2:03 AM|
|The bias pot operation should be able to be verified without the power tubes in place, or with them in but with the amp in standby mode, eg measure the Vdc on power tubes pin 5 whilst rotating the bias control over its range.|
Motorboating should be able to be stopped by removing the tube in V6, the LTP phase splitter, with negligible effect on the power tube idle conditions.
|tyler8611||5/31/2018 9:03 AM|
|tyler8611||5/31/2018 12:59 PM|
Now I'll remove the 6v6s and the phase splitter as you advised and then take the measurements with standby closed.
|tyler8611||5/31/2018 1:29 PM|
V1 pin 1: 211v
V1 pin 6: 221v
V2 pin 1: 199v
V2 pin 6: 192v
V3 pin 1: 469v
V3 pin 6: 469v
V4 pin 1: 202v
V4 pin 6: 191v
V5 pin 1: 393v
V5 pin 6: 471v
V6 pin 1: 215v
V6 pin 6: 252v
I checked the preamp cathodes and all except vibrato tube (no reading) and phase splitter (forgot to check) aligned with schematic voltages.
So next I will measure with the 6v6s installed and the phase splitter removed.
|tyler8611||5/31/2018 8:17 PM|
|tyler8611||5/31/2018 8:21 PM|
|Also, the B+ was 433, screens 429, PI 365, preamp 304. Preamp plates still running pretty high but maybe they'll drop when the bias is set right.|
|tyler8611||5/31/2018 9:28 PM|
|Would it be preferable to increase the range resistor value first? I have a 1.5k I can substitute.|
|Leo_Gnardo||5/31/2018 9:39 PM|
|g1||5/31/2018 9:40 PM|
|Are you sure about your 17mA idle current measurement?|
You said this was with -23V bias. Fender schem. shows -35V bias and with lower plate voltage. To me, that seems it would give much colder bias than what you have.
Regardless, with 17mA and 430V plate, you are idling around 60% of the 12W rating for 6V6. How hot do you want to go?
|tyler8611||5/31/2018 9:46 PM|
Do you think moving the range resistor value up is a good first move to try to get the bias current and negative voltage closer to normal?
|tyler8611||5/31/2018 9:53 PM|
|tyler8611||5/31/2018 10:08 PM|
|I was kinda concerned because I noticed earlier that my vib channel volume was for some reason up around 2-3, so I did this again just to be sure. |
No phase splitter:
Neg voltage -23
Max bias: 13.8 and 14.2
|tyler8611||5/31/2018 10:15 PM|
|Also concerning is the fact that B+ is going over 500v on standby- more than what the caps are rated for.|
|tyler8611||5/31/2018 10:23 PM|
|Leo_Gnardo||5/31/2018 10:23 PM|
Agree with the 6V6 brand choices. Old Sylvanias can be pretty good too.
Rated "26" on somebody's test rig. Of course tube vendors don't much talk about what voltages they apply to tubes under test, that's par for the course. If 26 is well lower than average, find out what's average and get a pair of those. It's not right to panel-beat output tubes into yielding good current figures by running the bias so low. Doing so has other effects, including severely limiting your clean headroom.
When you get around to measuring output power, I've seen healthy Deluxes range between 13 and 22 watts at clip. Don't be disappointed if it's near the low end. If the amp sounds robust when played that's close enough for rock 'n roll.
Hi voltage over 500 on standby, hmmm, how much over. 5 or 10 V, no problem. Just don't leave it on standby for extended periods. There's a 5AR4/GZ34 rectifier, right? That's a slow warmup type - it's actually safe to skip the so called warmup on initial switch on. Hi voltage won't be up to full for 15-20 seconds anyway. The overvoltage problem will be in evidence when you switch to standby with the amp warmed up. Also, it might be half an idea to use a 5Y3 instead, a "real" one, not the Russian made ones that deliver too much high voltage. 5Y3 aren't as efficient as GZ34, they'll leave you with a lower B+, a more relaxed sound, less to worry about. A bit less power but no biggie unless you're determined to get every last watt you can.
|tyler8611||5/31/2018 10:39 PM|
|tyler8611||5/31/2018 10:41 PM|
|tyler8611||6/1/2018 7:19 AM|
|tyler8611||6/1/2018 11:23 AM|
A bit less power is ok. As long as I get the tubes biased where they're supposed to be and the negative voltage closer to schematic.
Also hope the motorboating doesn't return. I guess that might indicate a bad coupling cap somewhere.
|tyler8611||6/1/2018 10:09 PM|
|pdf64||6/2/2018 3:35 AM|
|I wonder if something is wacky; with respect to circuit common 0V, what are the actual measured Vdc at the power tubes' terminals 3, 4, 5 and 8 at idle, without a tube in V6 socket.|
|Tom Phillips||6/2/2018 9:03 AM|
|I sense a basic misunderstanding.|
As stated above I agree that 17ma at your plate voltage may be fine. How does the amp sound at that setting? Listen with your ears not your DVM.
|tyler8611||6/2/2018 10:23 AM|
|tyler8611||6/2/2018 10:41 AM|
I did play through both channels last night. The normal channel sounded good. Worked normally. Vibrato was low volume but I didn't have the reverb driver or recovery installed because I had traced the motorboating to the reverb recovery stage. So I will have to change caps there or simply touch up a solder joint, although they looked good to me. It's either the .1 coupling cap or cathode bypass. It's not the tube.
Just out of curiosity, how do you check caps for leakage in the circuit? I never got nailed that down for sure. Then again never had a leaky cap.
Oh just for laughs, last night I found out my tweed deluxe picks up bluetooth. Nice bonus feature. That'll be the next mission- finding out how to prevent that. I wonder if the same trick used to eliminate RF would work?
|Leo_Gnardo||6/2/2018 10:50 AM|
Yes, any of the usual RF suppression techniques can be used in your tweed Deluxe. Many of these have no shield on the back side of the amp, and even the ones that have metal inside the back cover, don't have that metal grounded. That's where I'd start. And these days it seems cell phone chatter finds its way into practically every amp somehow.
|tyler8611||6/2/2018 11:34 AM|
Pin 3: 403, 405
Pin 4: 405
Pin 5: -20.9, -21
Pin 8: 15.9 mA (64.2 mV)
. 16.2 mA (65 mV)
|tyler8611||6/2/2018 11:45 AM|
The interference - I used to have an apple but switch to samsung just for the hell of it. This never happened with the apple. I was thinking of installing in the tweed deluxe a suppressor at the input, but I'd have to look up the best way to do that.
|tyler8611||6/2/2018 11:47 AM|
|tyler8611||6/2/2018 6:56 PM|
|I have an isolated problem with the V4 reverb recovery circuit causing motorboating. I substituted all the coupling caps and cathode bypass cap associated with V4. Nothing worked and I've tried four different 12AX7s- all the same result. I went in resoldered every point in the circuit.|
Could it be a bad filter cap?
|Tom Phillips||6/2/2018 7:21 PM|
|Yes. Most likely a bad fiter (decoupling) cap or bad grounding.|
|tyler8611||6/3/2018 7:58 AM|
|tyler8611||6/3/2018 11:53 AM|
|Tom Phillips||6/3/2018 12:43 PM|
|tyler8611||6/3/2018 12:47 PM|
|tyler8611||6/3/2018 1:56 PM|
|Went though and resoldered all the associated pins. Still motorboating from the reverb recovery. I traced the problem to V4. Tries Tried multiple tubes, changed all caps, same result.|
|tyler8611||6/4/2018 6:48 AM|
|I'm not actually sure if it's motorboating per se, but its definitely a loud low rumble. Never experienced before.|
|tyler8611||6/4/2018 7:05 AM|
|I wonder now whether the problem relates to the grounding of the 2nd filter cap. I tied it along with the PI and preamp filter caps, with a wire connecting to the copper bus. Perhaps I should have grounded it with the first stage at the PT bolt with the center tap.|
|Randall||6/4/2018 12:21 PM|
|I just built a DR, I connected C and D to a copper preamp ground bus, and the first three caps to chassis next to the PT. Mine is as quiet as a mouse.|
|tyler8611||6/4/2018 12:58 PM|
|tyler8611||6/4/2018 4:48 PM|
|tyler8611||6/5/2018 2:57 PM|
|pdf64||6/6/2018 9:51 AM|
|It may be helpful to record a clip of the motorboating issue, along with the effect adjusting any controls may have on it. Upload to youtube etc and provide a link.|
|tyler8611||6/6/2018 10:21 AM|
|tyler8611||6/6/2018 10:24 AM|
|I thought I'd had it traced down to the fact that my V4 to V5 heater pair was out of phase, but correcting that didn't cure it. All I have left to try is the V3 to V4 pair, which checks out good on continuity.|
|pdf64||6/6/2018 10:48 AM|
|With a balanced heater system, there a tiny theoretical benefit from arranging p-p power tube heaters in like polarity, but for the rest of the amp, I think it's immaterial; rather the guideline of lining up heater polarity for all the sockets seems akin to a good luck charm that everyone clings to because they don't want their amp to hum |
As there's a global NFB loop, the LTP phase splitter is really part of the power amp.
To help get your head around HT - 0V hum considerations, see The Valve Wizard
BF 0V arrangements are kinda random really, the fact that generally it works well may have been down to trial and error and good luck; hence it may be a good idea to review where your amp's 0V arrangement differs from a real BF.
|tyler8611||6/6/2018 11:34 AM|
|g1||6/6/2018 12:13 PM|
Heavy loading of the supply could also account for other odd issues.
How are you doing the current measurement (mA) ? Are you disconnecting the cathode resistor to do it?
Are the cathode resistors actually 1 ohm and do you measure around 65mV across each at idle with no signal?
|tyler8611||6/6/2018 12:21 PM|
|tyler8611||6/6/2018 12:31 PM|
|Just a reminder, the normal channel plays fine with V4 removed. The rumbling goes away. But no sound from vib channel at any setting.|
|tyler8611||6/6/2018 12:38 PM|
|tyler8611||6/6/2018 4:25 PM|
|I've recorded it but I don't know how to post it on here.|
|tyler8611||6/6/2018 4:59 PM|
|I had hooked it up to a different speaker that I could hear better. Definitely motorboating.|
|g1||6/6/2018 6:08 PM|
|You have to disconnect the cathode resistor if you want to measure mA current directly. Current measurement must be done with the meter in series. The point of having the 1 ohm cathode resistors is so you don't have to 'break in' to the circuit and can just measure voltage in mV across the resistor.|
So your mA numbers are not valid. Your measurement of 65mV across the resistor is what you should go by. 65mV divided by 1 ohm equals 65mA idle current. At 400V plate, you are idling those tubes around 26watts. If you are lucky they may still be ok.
Somewhere around 20mA is probably more appropriate, which will measure as 20mV across the 1 ohm resistor.
|tyler8611||6/6/2018 6:46 PM|
So this way of measuring across the 1 ohm is invalid and the resistor would have to be pulled from ground?
|Leo_Gnardo||6/6/2018 7:00 PM|
Something's not right about the math also, 411V x .0666A = 27.4W, way in excess of a 6V6's 12W plate dissipation rating. We might expect that if the bias voltage on the control grid is -15.9V. Quite a lot less than the -35ish volts that's expected. Similar for the other 6V6. At that rate they should be glowing orange, ow!
|tyler8611||6/6/2018 7:09 PM|
One of them is glowing blue, but that's it.
|g1||6/6/2018 8:10 PM|
If you want to leave the 1 ohm resistor in circuit, you can only do voltage (mV) measurements with your meter.
Turn down the idle current till you have 20mV across the 1 ohm resistors. What is now the grid voltage at pin5 of the power tubes? What is the plate voltage at pin3?
Is it still motorboating?
|Enzo||6/6/2018 8:18 PM|
|I don't worry about the 1 ohm diode accuracy. I think I bought 1% ones just for the form factor. But so what if they are off 5%? If we have say 30ma current, a 5% margin is just a milliamp and a half.|
|tyler8611||6/6/2018 8:55 PM|
|g1||6/7/2018 12:16 PM|
|That sounds much better for idle current. You are now at about 9watts or 65% dissipation. You can see how much the heavy current had been pulling down the plate voltage. And you are at -35V at the grids just like the schematic (rather than the -20V you reported earlier).|
Does the normal channel function properly with V4 pulled?
|tyler8611||6/7/2018 2:39 PM|
Vibrato channel- can only hear scratchy notes with volume at max. Vibrato does not kick in, even though the roach blinks, tube is good and voltages look normal.
|g1||6/7/2018 5:46 PM|
|Ok. Motorboating and tremolo are not that far off from eachother. |
Can you try disconnecting the wire that goes from the intensity pot to the .1uF/220K junction?
|tyler8611||6/7/2018 6:34 PM|
|tyler8611||6/7/2018 8:42 PM|
|tyler8611||6/7/2018 8:46 PM|
|g1||6/7/2018 9:19 PM|
|I'm not sure if you mean the reverb and volume pots are not working? Or everything is functional except no trem? (aside from hum and hiss issues)|
|tyler8611||6/8/2018 5:15 AM|
Reverb is always in the signal in a very heavy amount. Neither turning rhe pot nor pushing the footswitch changes the reverb in an any way. It's always on, a lot of it.
|g1||6/8/2018 1:39 PM|
|It would help if you could post some clear pictures of the board, pots, etc. so we can check the layout & wiring.|
|tyler8611||6/8/2018 2:25 PM|
|tyler8611||6/8/2018 3:33 PM|
|g1||6/8/2018 5:45 PM|
|When you have the reply box open, click on 'go advanced' (below the box). Then scroll down to 'manage attachments' and click on it. From there you should be able to add what you want.|
|tyler8611||6/8/2018 5:48 PM|
|tyler8611||6/8/2018 6:04 PM|
|Going to have to make my files smaller.|
|tyler8611||6/8/2018 10:37 PM|
|tyler8611||6/8/2018 10:47 PM|
|tyler8611||6/9/2018 6:38 AM|
|I have one more pic of the inside, showing the output components, tube sockets and PT- facing the back of the chassis. Wouldn't let me post for some reason. It's under 3mb. I'll keep trying.|
|tyler8611||6/9/2018 6:43 AM|
|tyler8611||6/9/2018 6:45 AM|
|That's all I took. Not the neatest work, obviously and I can't believe I forgot to put the twisted pair from the vib channel input grid through the proper hole. But I can always fix it later.|
|tyler8611||6/9/2018 6:52 AM|
|V4 Motorboating clip|
|g1||6/9/2018 11:33 AM|
|That big orange drop cap connected to the tremolo bug, what value is it? (and why?).|
Does it make any difference it it is removed or disconnected at one end?
|tyler8611||6/9/2018 11:36 AM|
|g1||6/9/2018 11:44 AM|
|Ok. It looked bigger to me. I thought maybe it was a .1uF. So you tried with it lifted and no difference?|
And you did say that you could see the bulb flashing?
|tyler8611||6/9/2018 11:46 AM|
|tyler8611||6/9/2018 11:47 AM|
|Tom Phillips||6/9/2018 1:02 PM|
You posted really nice high resolution photos. Would you please include at lease one photo that shows the whole gut shot as a single view?
|tyler8611||6/9/2018 1:33 PM|
|tyler8611||6/9/2018 1:41 PM|
Had to crop it to get it under 3mb.
|galaxiex||6/9/2018 3:03 PM|
I use BUZZ 3D Media converter to convert images and reduce file size.
It works great but you are limited to 1280X1024 PNG or JPEG output.
Not really a problem as far as size goes, still decent.
It's an older program... there may be better/newer ones out there.
Oh ya, it freeware.
|shortcircuit||6/9/2018 5:09 PM|
|Here's a stacked image of a working 65 deluxe reverb (bottom photo) , compared to your build , hope it helps , g1 in#117 asked my first question, orange drop (is that the new LIKE)[ATTACH=CONFIG]49222[/ATTACH][ATTACH=CONFIG]49223[/ATTACH]|
|dstrat||6/9/2018 5:32 PM|
|tyler8611||6/10/2018 1:15 AM|
|tyler8611||6/10/2018 11:46 AM|
|Touched up the pots and grounds and eliminated the cap on the roach. Going to see if it makes ant difference.|
|tyler8611||6/10/2018 2:18 PM|
|Well guys, it's fixed! The last few things I did were touch up the pots and grounds, and I removed the .022 cap from the trem roach, which may well could have been the cause. I appreciate you all giving advice along the way! |
Got it biased at 20mV with 444 plate voltage. Sounds excellent.
|tyler8611||6/11/2018 7:21 AM|
|Now I need to find the cause of this ratty distortion that's like a tearing sound that I get when vibrato channel is on 10. It's not the speaker and not V1 or V2. Maybe one of the other preamp tubes. I already swapped JJ 6v6s and it made no difference. Aside from that, the amp is running just fine and sounds really good!|
|SoulFetish||6/11/2018 10:38 PM|
The important thing to remember when making this alteration is this: In order to maximize the mojo, use an inexpensive and reliable economy cap for this.
|tyler8611||6/12/2018 4:35 PM|
|tyler8611||6/12/2018 6:27 PM|
|g1||6/12/2018 6:33 PM|
|Yes, that should be fine. |
(edit) That's about 9W idle which is about 70% of the 12W that 6V6 are rated at.
(65% of the 14W a JJ 6V6 is rated at)
|SoulFetish||6/12/2018 6:37 PM|
|SoulFetish||6/12/2018 6:40 PM|
|I’ve seen 6V6s rated for both 12W and 14W. The 70% figure I quoted was at 12W.|
|g1||6/12/2018 6:50 PM|
I've edited my previous post for the 12W version. If he's using JJ's, he can use the 9 over 14 = 65% figure.
|tyler8611||6/13/2018 7:48 AM|
|Thanks for the help guys. The only issue I have now is this sound like speaker cone tearing (though it isn't) when I dime the vibrato channel. It is a ripping sound that spurts around after sustaining a chord. Happens with or without the effects. I've changed V2 and it's still there. Again, only happens on 10.|
The 6v6s are almost new JJs. The one nearest the rectifier has a slight blue glow around one of the spacers and the blue actually intensifies when I play a note or chord on 10.
Guess it's either that power tube or something internal. I swapped preamp tubes and also hooked up to a different speaker with the same result.
|pdf64||6/13/2018 8:01 AM|
|tyler8611||6/13/2018 8:11 AM|
|tyler8611||6/13/2018 3:15 PM|
|I will note that, with the chassis out of the cab, it doesn't exhibit any tearing sound. I warmed the bias back up from 18 mA to 20, so it's either that or the cab that's causing it perhaps.|
|tyler8611||6/13/2018 3:27 PM|
|I did barely tuck the wires into proper place but not much. They were good already. Who knows. I have it back in the cab so we'll see.|
|tyler8611||6/13/2018 3:45 PM|
|The cab is causing it, apparently. That's when it returns.|
|tyler8611||6/13/2018 3:47 PM|
|g1||6/13/2018 6:22 PM|
|I can't really make out the bad noise from the soundfile, but I don't have much for speakers.|
Often, a fault that shows up only in cabinet is due to vibration. Could be a bad tube, bad tube/socket connection, bad solder joint, dirty pot, etc.
I would try applying a constant signal with the chassis out of the cab, then tap around the chassis with a chopstick or rubber mallet or something and see if you can recreate the problem.
|tyler8611||6/14/2018 7:44 AM|
I'll go back in and do a more thorough check. I didn't observe anything odd when I poked around the lead dress previously. Would it more likely be caused by V2 or the 6v6s?
|g1||6/14/2018 1:59 PM|
|It could be any tube. When it's doing it in the cab you can hold the tubes with a clean rag (don't burn your hand!) one at a time and see if you can make it stop. You can use a clean oven mitt too.|
|tyler8611||6/14/2018 2:23 PM|
|tyler8611||6/14/2018 2:26 PM|
|jmaf||6/14/2018 2:43 PM|
One other thing: if this is getting worse in the cab, means that when the tubes are upside down it gets worse, then there can be mechanical problem in the tubes.
Also tubes are microphonic, they can be obnoxious when in a cabinet, the speaker shakes the tubes which replicate the vibration in the output, this matches what you describe when you play a chord, the underlying vibration.
|tyler8611||6/14/2018 2:47 PM|
|jmaf||6/14/2018 3:10 PM|
What you describe, above volume 8 on sustained chords clearly sounds like feedback through the tubes, chassis vibration coming back through the tubes, etc. Could be a bunch of things.
|tyler8611||6/14/2018 3:27 PM|
|g1||6/14/2018 3:32 PM|
|jmaf||6/14/2018 7:16 PM|
Once he swaps tubes I guess we'll get a better idea.
|tyler8611||6/17/2018 10:41 AM|
|Hey just wanted to finally update, busy weekend. The problem was solved by a swap. It was either the tremolo tube or phase splitter, since I did those at the same time. No more harsh ripping!|
|Tone Meister||6/17/2018 8:02 PM|
|Steve A.||6/17/2018 11:28 PM|
|tyler8611||6/18/2018 5:28 AM|
I'll reinsert the old phase inverter and trem tube and find out for sure. Honestly I just felt like playing once I heard the ugly distortion had gone. Thanks guys!
|tyler8611||6/18/2018 5:30 AM|
|1ampman||6/18/2018 6:55 AM|
|Lack of high voltage is caused by open equalizing resistors under the circuit board under the dog house. You need to flip over the cap circuit board to get to them 220K 1W|
|Tone Meister||6/18/2018 3:36 PM|
This place is a cornucopia of in-depth technical knowledge. The best-of-the-best techs, designers, and engineers in the world unselfishly offer their assistance on this site, and I think we owe it to the next guy to clearly show the resolutions in our threads, including info on hard to find parts and non-conventional problem solving. In the end, it saves bandwidth and many times keeps the pros here from answering the same questions multiple times.
So yes, please do swap those tubes back in there (hope you know which one went where ) so you can put a lid on this one.
|tyler8611||6/20/2018 7:56 AM|
I'm finally going to have time today to swap the tubes back in one at a time in order to find out for sure which was the problem and report back.
I've had maybe two or three hours to play it since I sorted the problem. Sounds really great. No noise problems or grounding issues. All settings work properly, the effects are flawless. I'll see if I can record a clip through my interface or phone.
Not sure if I posted pics of the tubes or transformers, but I'll go over that. PT is from Classictone. It's running 25-30v over schematic voltages. Maybe a mojotone would have produced a lower voltage but from the spec sheet, the classictone looked like it would. Choke and OT are mojotone.
V1: rca 7025
V2 : rca 7025
V3: jan philips 12at7
V4: rca 7025
V5: EHX 12ax7 (replaced tung sol)
V6: mullard ecc81(replaced jan 12at7)
V7 and V8: JJ 6v6
V9: JJ GZ34
Speaker is a Weber 12F150 25w, no dope.
|tyler8611||6/20/2018 4:10 PM|
|Just did a swap and confirmed it was the previous phase inverter tube causing the bad distortion.|