|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.