BF Fender Vibrochamp questions

[g1]

Have you tried another tube there?

[nosaj]

Have you tried another tube there?

I have a few others that all exhibit the roughly same voltages. I can try them with the cap lifted. So far I've just been using the JJ I just bought last month.

nosaj

[g1]

If you've had the same high cathode voltage with other tubes, then it's probably not the tubes. Just wanted to make sure you had tried more than one when dealing with this excess current issue.
Not ready to rule out the coupling cap, do you have another that you can swap in there?

[nosaj]

If you've had the same high cathode voltage with other tubes, then it's probably not the tubes. Just wanted to make sure you had tried more than one when dealing with this excess current issue.
Not ready to rule out the coupling cap, do you have another that you can swap in there?

Definately got parts to play with. I think I'll put the cap in and swap out the 220k separately of course taking measurements in between.

thanks,
nosaj

Just curious about your moniker G1 I understand but is it because with a little kick you get louder?
Mine is just my name backwards

[Chuck H]

Well, since the power tube plate voltage is the same with the cap lifted and the reading at the end of the lifted cap seems to be the meters default/null I actually don't suspect the cap at all (But never invent reasons to NOT test something. Thank you Enzo).

[danman]

I was reading through this thread and noticed that in post #23 you mentioned that the B+ measured 468vdc with no 6v6 installed, and 291vdc with a 6v6 installed. Something still seems off if your voltage has dropped that much with the power tube installed. Was this a fresh 6v6?

[Chuck H]

I might suspect the old, original filter cap can, except that if it were a shorted filter cap you would see some anomalous voltage drop even with the power tube out. So even though it SHOULD be replaced, I don't think it's shorted. And I don't think it's the coupling cap leaking because the voltage tanks even when it's lifted. I don't suspect the OT because it's new and meters out ok. Even for a conductive circuit board to be causing the problem, there should be some indication of voltage on the power tube grid greater than it is.

I'm starting to suspect a wiring error.?.

[nosaj]

Well, since the power tube plate voltage is the same with the cap lifted and the reading at the end of the lifted cap seems to be the meters default/null I actually don't suspect the cap at all (But never invent reasons to NOT test something. Thank you Enzo).

Ok I replaced the cap with an orange drop and a new 220k resistor. Voltages the same so I try to make some noise with a guitar no noise. I'm doing this with the chassis half in half out as it allowed me access for measurements. So I slide it in a little more test voltages voila! sound good voltages. So I play a little harder on the heavier strings (humbucker pickup) can make it kinda fuzz out and any input dies so I check voltages on the 6v6 and voltages are still reading good but when I touch the resistor 1.5k resistor (grid stopper? ) the sound comes back because the strings were still vibrating.

So if because of me using the chassis half in half out would an intermittant speaker connection cause these symptoms.

Cause the way I understand it the OT acts similar to a balanced seesaw right tube right speaker level seesaw efficient output. But if I stretch the speaker connection a bit making intermittant contact once side of the seesaw goes bonkers?

Am i ontrack or did I jump the tracks in what I'm thinking?

I'm going to make the speaker connection longer in the interim. The chassis holder I made is in use and not small enough for these amps. So I guess I'm going to build a second one smaller format.
Oh and i'll post the voltages after I go grab them.

nosaj

[Chuck H]

I was reading through this thread and noticed that in post #23 you mentioned that the B+ measured 468vdc with no 6v6 installed, and 291vdc with a 6v6 installed. Something still seems off if your voltage has dropped that much with the power tube installed. Was this a fresh 6v6?

This is exactly the issue we've been covering. Other tubes have been tried, some circuits and conditions have been tested.

[nosaj]

Ok I replaced the cap with an orange drop and a new 220k resistor. Voltages the same so I try to make some noise with a guitar no noise. I'm doing this with the chassis half in half out as it allowed me access for measurements. So I slide it in a little more test voltages voila! sound good voltages. So I play a little harder on the heavier strings (humbucker pickup) can make it kinda fuzz out and any input dies so I check voltages on the 6v6 and voltages are still reading good but when I touch the resistor 1.5k resistor (grid stopper? ) the sound comes back because the strings were still vibrating.

So if because of me using the chassis half in half out would an intermittant speaker connection cause these symptoms.

Cause the way I understand it the OT acts similar to a balanced seesaw right tube right speaker level seesaw efficient output. But if I stretch the speaker connection a bit making intermittant contact once side of the seesaw goes bonkers?

Am i ontrack or did I jump the tracks in what I'm thinking?

I'm going to make the speaker connection longer in the interim. The chassis holder I made is in use and not small enough for these amps. So I guess I'm going to build a second one smaller format.
Oh and i'll post the voltages after I go grab them.

nosaj

Here's the deal Holyfield

Upon opening the rca speaker jack. And opening the holddown. The negative connection(ground) the jack was not scored before soldering the ground wire to the jack. It's been playing The Cult for about the last 2 hrs on 8(vol still going strong). I need to hook up the Octal test plug to read voltages while it's running.. I get the voltages and forget to write them down but they been in the 470's with tube plugged in.

Hopefully I'm at the end of the road.

Thanks so much,
nosaj

[g1]

Glad to hear you got it sorted out. Sounds like any pressure (on chassis or grid stopper) was correcting the bad connection. From the way the cathode current was going high, and the big drop in B+, I would guess the power tube was breaking into oscillation.

Just curious about your moniker G1 I understand but is it because with a little kick you get louder?

g1 is the control grid for tubes and commonly the input. So my input to the forum. That's part of it anyway.
Not sure what you mean about the little kick thing?

[nosaj]

Glad to hear you got it sorted out. Sounds like any pressure (on chassis or grid stopper) was correcting the bad connection. From the way the cathode current was going high, and the big drop in B+, I would guess the power tube was breaking into oscillation.


g1 is the control grid for tubes and commonly the input. So my input to the forum. That's part of it anyway.
Not sure what you mean about the little kick thing?

A little kick or a little alcohol makes you louder?
my odd sense of humor.

nosaj

[Chuck H]

We had a simulpost (also thanks Enzo). You were already on the same track A fault is the "basically" the same as a wiring error when you know the components are correct I suppose.

DO resolder connections with fresh solder. Suck the old stuff out if you have any kind of sucker. Clean ALL the contacts for the jacks and speaker connections.

Most important...

So I slide it in a little more test voltages voila! sound good voltages.

What are the operating voltages now?

[nosaj]

We had a simulpost (also thanks Enzo). You were already on the same track A fault is the "basically" the same as a wiring error when you know the components are correct I suppose.

DO resolder connections with fresh solder. Suck the old stuff out if you have any kind of sucker. Clean ALL the contacts for the jacks and speaker connections.

Most important...



What are the operating voltages now?

So I goto get the voltages and they're back to the 300s.

So I'm thinking filtercaps not proving enough voltage and crap out with a load someone I think suggested it.

So I desolder the connections on the cap can. I've only seem to have 3 16uf 450v new caps on hand, so I'm thinking they should be ok. Twist all the negative ends together and solder them together, then pull out the weller and solder the negatives to a chassis ground point. Put one of each lead to each cap and solder them on.

Powered up on dim bulb tester bright them dim when the caps charged so ok there.
Put it on live voltage When its all powered up the amps meter is bouncing on the variac voltages are bouncing from 468 down to 350. Pull the power tube and it stops. Try another 6v6 same issue.

Do I not have enough capacitance for the circuit? When the its bouncing you can feel it in the amp but not hear it through the speaker.
Also heard back from magnetic components heres the info on the transformer which is about what I got on readings
Here is the nominal primary DCR:
Pri DCR = 253 Ohms (5K Ohm tap)
= 334 Ohms (8K Ohm tap)

Driving me nuts

nosaj

[Chuck H]

If the old caps are partially shorting and also not capacitor-ing (holding charge) that might explain the anomalous behavior with paralleled caps. I think you need to bypass the old caps completely for an accurate test. 16uf is fine for function and won't affect the voltages significantly. Worst case with that value is a little more hum, but not failing operation and drifting voltage.