|nosaj||6/18/2017 11:02 AM|
|Carvin vintage 16 low output|
I was given a Carvin Vintage 16 that someone did these mods to
It has low nasty output. While going over the document and touching up cold joints. I noticed on V5 it looks like pin2 and 3 were tied together. I don't see it on the schematic or on any other EL84 amps. V4 is not that way. Any legitimate reason for this? I think it is wrong and should be removed.
|g1||6/18/2017 11:13 AM|
|If grid is connected to cathode, then yes, that would be a problem.|
You don't mean pins 3 & 4? That could be done for a few reasons.
Not sure what you mean about mods, are they shown on that schematic or referenced elsewhere?
Edit: never mind about the mods, I missed the first link in your post.
|nosaj||6/18/2017 11:29 AM|
I've included a shot of it.
|g1||6/18/2017 11:40 AM|
|Basing diagram is bottom view, so that would be 7 & 8?|
If you had grid grounded (2 to 3) you would lose bias and redplate.
7 is plate, I don't know why anyone would tie it to anything. 8 is supposed to be internal connection so it should not be used.
|nosaj||6/18/2017 11:41 AM|
|Justin Thomas||6/18/2017 11:41 AM|
|Isn't that pins 7 & 8? Either way, if that's a 12AX7, it's still grid-to-cathode...|
|g1||6/18/2017 11:48 AM|
|Yes I would think so. But much less damaging this way.|
|nosaj||6/18/2017 1:19 PM|
It crackles a lot which disappears when tube is removed. (tube is V3 phase invertor With tube removed I can inject signal at the plates and it's clean.)
I reflowed the solder on all suspect joints and the header connector. Still crackles. makes me think resistors since the plate resistors are good because of audio injection that would leave the cathodes.
Am I headed in the right direction or am I lost and don't know it yet?
Thanks so much
|Enzo||6/18/2017 1:33 PM|
|Why stop with V3? Pulling that suggests the problem is before it, so put it back and pull V2, any affect? If so, pull V1, same question. Oh, I don't see a V2, is that a reverb or something?|
|nosaj||6/18/2017 2:37 PM|
|g1||6/18/2017 3:12 PM|
|Does volume or treble pot affect it?|
|nosaj||6/18/2017 3:26 PM|
Pull V2 noise still there. grounding grids on V1 no effect. My thinking is issue is somewhere before V3. Resistors are most likely for crackly scratch noises?
No DC on output.
V1 pin1 177vdc pin3 .809 pin4 1.88 pin6 159 pin8 .01
v2 pin1 124.8 pin3 .471 pin6 170 pin7 -.03 pin8 .272
v3 pin1 210 pin2 30.7 pin3 47.49 pin5 208 pin6 32 pin7 45
v4 pin1 -10.36 pin2 -10.36 pin7 278 pin8 .02 pin9 277.1
V5 pin1 -10.36 pin2 -10.36 pin7 279.2 pin9 276
OT red 281
brown v5 279
Blue V4 279.
I'll check the resistors before the PI. And DC on the Volume pot.
|g1||6/18/2017 6:57 PM|
|If the volume control can kill it, it must be before that. (correct me if volume doesn't completely kill it)|
Pulling V1 doesn't get rid of it, so it must be after that. Which leaves C7, C34, less likely but possibly the volume pot, R4, C33, R41 (and associated connections).
And to completely rule out the reverb tube, you can try grounding C18 (at R8 end).
|nosaj||6/19/2017 6:16 PM|
There is DC on the vol pot. one of the new caps is leaking .5 dc onto the pot. I'll replace it and report back.
|g1||6/19/2017 7:53 PM|
|Sorry I missed the boat on that, I was going by the stock schematic and didn't realize how extensive the mods were or that even the names of the controls were changed.|
What were you referring to as the volume control, the PPIMV ?
|nosaj||6/20/2017 4:35 AM|
|g1||6/20/2017 11:46 AM|
|One other thing I was going to mention was to check on the bias. The stock schem. says -17V on the grids and I think you mentioned -10V ?|
I guess any leakage could be affecting that also, but double check after the cap fix.
|nosaj||6/20/2017 6:30 PM|
I have never taken a dual pot apart before. ( but I will be soon) I don't yet understand how I'm seeing voltage on both, I really thought they were separate pots with a common knob.
|nosaj||6/20/2017 7:34 PM|
I think instead of messing around with someone else's mode. I'm gonna move it back to stock and see how things go from there.
Not really sure I'm a fan of master volumes I tend to like loud and nasty.
Will follow up tomorrow.
|Enzo||6/20/2017 7:37 PM|
|There is a difference between a leaky cap putting voltage on a node and a DC voltage appearing on a node a cap connects to. Remember those conductive eyelet boards on old Fenders?|
I see the factory schematic, and I see a printed up description and instructions for mods, but is there a schematic of your amp AS BUILT? I can imagine about where this double pot is, but I want to see the circuit, I am suspicious you may have an unterminated part.
|nosaj||6/20/2017 7:39 PM|
|nosaj||6/21/2017 5:24 PM|
The blue and the yellow ones on the left have dc that goes from .5 up to 3volts not in any order I can see. The 2 on the right no DC at all. It's starting to storm again TS Cindy is dumping a tone of rain on us.
I'll grab the voltages on the mounted side of the cap. In my head I should see no dc on the flying ends. I am using chassis ground.
|nosaj||7/7/2017 7:48 PM|
No DC on the Volume now.
Checking voltages on caps C18 C19 and C20 I have DC on both sides of the caps.Going by the Carvin schematic It looks like c18 and c20 need to be replaced C19 maybe seeing DC on both sides because c18 failed.
Does this look right as far as my thinking?
Can't replace anything till tomorrow evening.
Also with C22 and C23 being .1uf instead of .047 what effect would this possibly have on sound? I still plan on changing it but just curious.
|Enzo||7/7/2017 11:35 PM|
|C22 larger means more bottom end is possible. Someone else can do the math to see where it matters.|
WHAT DC voltage? A quick in my head tells me the cathode of the tube will have a good 50v or more on it. So C19 would have 230v on one end and 50 on the other. So C18 would also have 50v on one end and zero DC on the other. C20 ought to have the 50v on one end and the other end maybe 6 to 10v from that 3.3k resistor.
C18 has voltage n both ends?
|nosaj||7/8/2017 2:00 PM|
C19 270 Vdc / 42 Vdc
C20 44Vdc / 4 Vdc
Guess I was confused with Voltage on C20, thought that you wouldn't have DC on Grids of any preamp.
|Enzo||7/8/2017 3:55 PM|
|Grid voltage is considered with respect to cathode voltage. You are measuring those grids to ground. The "real" voltage there is higher than that. The grid voltage will only be a volt or so more negative than the cathode. The fact that both of them are about +50 is irrelevant to the tube.|
But I don't understand your C18 readings. On the schematic I see the right side of C18 connects to the grid and C19, your 42v. That leaves the left end of C18. Where would 300v come from? If the cap were leaky or shorted, then all we would see would be the 42v. I see no component failure that could put 300v there. If it really is at 300v, then it almost has to be some sort of short on the board, like wires touching, or a bead of solder, etc.
|nosaj||7/16/2017 1:41 PM|
Now C36 measures 229v on one side and 240v on the other. Does that sound right?
It is shown on the Carvin schematic one side connects to r8 and c18 other side connects to r8 and c41 and c12.