BF Fender Vibrochamp questions

[nosaj]

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.

Thing is I didn't parallel them in, just outright bypassed the original can and with the 16uf the voltage would go up and and down(oscillate) consistantly. Wire it back to the can no oscillation) I have a jj 32uf 32uf can I can try this afternoon to check.

nosaj

[The Dude]

Ok, I may have missed it. I only skim read the thread, so apologies if I did. I still don't see a cathode voltage or the voltage drop across the cathode resistor. Is it here and I missed it? We need that for a couple of reasons. 1) We could have a leaky/shorted cathode cap. 2) It will tell us idle current (if the cap isn't bad).

Edit: Oh, never mind. I found it in post #35. Sorry. According to that post, you have over 100ma idle current. Have you tried raising the value of the cathode resistor?

[nosaj]

Ok, I may have missed it. I only skim read the thread, so apologies if I did. I still don't see a cathode voltage or the voltage drop across the cathode resistor. Is it here and I missed it? We need that for a couple of reasons. 1) We could have a leaky/shorted cathode cap. 2) It will tell us idle current (if the cap isn't bad).

Edit: Oh, never mind. I found it in post #35. Sorry. According to that post, you have over 100ma idle current. Have you tried raising the value of the cathode resistor?

No i have not any suggestions on a value? It's 470r now.

Thanks,
nosaj

[Justin Thomas]

It won't hurt if you overdo it... I have an 820R in my Champ w. B+ of 430. Could try up to 1.5K prolly.

Justin

[nosaj]

It won't hurt if you overdo it... I have an 820R in my Champ w. B+ of 430. Could try up to 1.5K prolly.

Justin

Let me see what I have on hand. Just soldered in the 32uf JJ cap cans. Good voltage till 6v6 is installed.

So let me find a resistor and tack it in.

Thanks,
nosaj

[The Dude]

Keep in mind that you may have to up the voltage of the cathode cap to adjust for the larger value resistor.

[nosaj]

Keep in mind that you may have to up the voltage of the cathode cap to adjust for the larger value resistor.

Somewhere I read that for example upping the cathode resistor to say 1.5k youd need to up the cap to say 50uf for frequencies to be equivalent to say a 470R and 25uf cap.

Is this logical or correct or just some mojo smoke?

Thanks,
nosaj

I have onhand a 1.5k 10watt and a 47uf/400v film cap

[Chuck H]

It's the other way around. You could actually use a lower capacitance with the higher resistance for the same frequency knee. But don't trouble about it. 25uf is fine either way. What you may want to trouble about is the voltage rating, as Dude said, and locating that cap somewhere with less heat than bridged over the resistor (which gets hot).

I'm still not convinced that bumping the cathode resistor is the right move. Every other Champ (other than Justin's I suppose) is working fine with the 470R cathode and still has a B+ of 420-ish V. I still think something is askew. Why, all of a sudden, would every Champ need twice the value for the cathode resistor? Well, they don't. But something about YOURS means YOURS does. What is it? That's what needs to be changed.

[Justin Thomas]

I never said mine was fine... it's a dirt machine! But it doesn't blow up, so I use it as such. I mainly kept supping the resistor cuz I didn't want to take TOO much of a chance torching all my old 6V6GTAs. But no, I don't know if it's "right..."
I should probably poke around inside with this thread in my hand...

Justin

[nosaj]

It's the other way around. You could actually use a lower capacitance with the higher resistance for the same frequency knee. But don't trouble about it. 25uf is fine either way. What you may want to trouble about is the voltage rating, as Dude said, and locating that cap somewhere with less heat than bridged over the resistor (which gets hot).

I'm still not convinced that bumping the cathode resistor is the right move. Every other Champ (other than Justin's I suppose) is working fine with the 470R cathode and still has a B+ of 420-ish V. I still think something is askew. Why, all of a sudden, would every Champ need twice the value for the cathode resistor? Well, they don't. But something about YOURS means YOURS does. What is it? That's what needs to be changed.

Well its not the filter caps as I've subbed that and watched the same issue happen, Different 6v6's same issue.

I'm open to any suggestions. The only mod done to this was the grid limiter and screen resistor.
Is this something else to consider? When I replaced the OT instead of the 5 watt original style they offered I chose the 15watt SE as it was also listed for a vibrochamp on their site?

I also found that laying the cab on its face the cabinet holds the chassis with complete access.

Thanks,
nosaj

[nosaj]

Well its not the filter caps as I've subbed that and watched the same issue happen, Different 6v6's same issue.

I'm open to any suggestions. The only mod done to this was the grid limiter and screen resistor.
Is this something else to consider? When I replaced the OT instead of the 5 watt original style they offered I chose the 15watt SE as it was also listed for a vibrochamp on their site?

I also found that laying the cab on its face the cabinet holds the chassis with complete access.

Thanks,
nosaj[ATTACH=CONFIG]41018[/ATTACH][ATTACH=CONFIG]41022[/ATTACH][ATTACH=CONFIG]41019[/ATTACH][ATTACH=CONFIG]41020[/ATTACH][ATTACH=CONFIG]41021[/ATTACH]

Well I put the 1.5k 10watt and a 47uf 400v just for testing purposes


v1 pin1 208vdc pin6 204
v2 123vdc- 187vdc pin6 335 pin7 135 - 194 pin8 127- 188
v3 pin3 350 pin4 352 pin6 372 pin8 96v

. Have not subbed the 5y3 any thoughts on it being problematic?

Thanks,
nosaj

[eschertron]

Well I put the 1.5k 10watt and a 47uf 400v just for testing purposes
v3 pin3 350 pin4 352 pin6 372 pin8 96v

65ma, just shy of 20W tube dissipation?! How long before the plates or screens glow/melt/implode?
Or are we seeing something related to the socket, and not the (variously tested) tubes?

[The Dude]

If still have that much idle current with a 1.5k, I would say there is definitely something wrong. I would double check all wiring to the output tube socket. Make sure each pin is wired where it's supposed to be. Does it look like it's been messed with?

[Chuck H]

Pretty sure I see some miswiring. It's hard to see everything well in the pics, but I'll open with seeing pin 6 being soldered to pins 4/5 (filament) on the tremolo circuit (V2b)

[pontiacpete]

Referring back to your photos of the power tube socket. What is connected to pin 6? Something looks strange in this area to me .
Or is it just the picture?
There should only be one wire there for the screen voltage and that 470R that connects to the other end of the resistor to pin 4.