Happy Vibro Champ

[Justin Thomas]

I blew a pair of EH6V6s in 10 minutes with my 79 "Vibro-"Champ (in quotes cuz I MADE it one) with ~430 on the plates (not accounting for cathode voltage). Pretty sure I had a 680/10W in there... using JJs or UOS pulls, no problems since! Or I plug in a 6L6 for some more guts, and the 20W Emi speaker helps... The nice part is, the Champ & VChamp & Princeton (non-verb) all share a PT, so no worries about heater current!

Justin

[shortcircuit]

The last Champ I looked over had "just" enough PT current capacity and the owner had "just" enough coin that we upgraded the OT and installed an EL34 Along with some other circuit mods I have to pat myself on the back and say it was the bees knees tonally.

I know from experience that Champs with the stock value bias resistor will eat tubes. I've blown up a couple of 6V6's with the cranked up test in the stock amps after servicing. A sturdy 6V6 is an option, but if the amp can't use any common 6V6 then it's just cumbersome. Better to bias it cooler.

Finally got the time to complete cap job , left the 825ohm cath resistor in for now, so it's biased down. It is the quietest vibro champ , very little vibro champ buzz/hum, no loss of usable tone. I think it's a happy vibro champ
Thanks to everyone for there input , support on this forum is nothing but impressive

[Leo_Gnardo]

I blew a pair of EH6V6s in 10 minutes

True EH 6V6 won't put up with the 100% & beyond biasing in Champs. Those who can scrounge up an old but working RCA or Sylvania will have better luck. And of course the current JJ 6V6 is an extra tough contender but I've seen those also go to an early grave in this application.

[Justin Thomas]

I don't think it was the bias in my case; I think it was the screens melting. The first one didn't have time to redplate. Two strums at "full-tilt whackage" and zzzzzzzt, fuse blew.

I actually kept this one biased cooler than 100%, closer to maybe 80%.

Justin

[shortcircuit]

True EH 6V6 won't put up with the 100% & beyond biasing in Champs. Those who can scrounge up an old but working RCA or Sylvania will have better luck. And of course the current JJ 6V6 is an extra tough contender but I've seen those also go to an early grave in this application.

Just heard back from EH to make sure my facts were correct ,the EH 6V6GT's I'm using were manufactured in Dec 2000 , I bought them new so they've survived the hot bias , bad caps for 18yrs. Granted it was only used in small clubs, studio and practice , none the less they've been used and abused. Even the losers get lucky sometime , I won't elaborate on whether that's EH or me. I do how ever have a good stock of vintage 6V6's and do appreciate your input and advice. Thanks All !!

[Leo_Gnardo]

Just heard back from EH to make sure my facts were correct ,the EH 6V6GT's I'm using were manufactured in Dec 2000 , I bought them new so they've survived the hot bias , bad caps for 18yrs. Granted it was only used in small clubs, studio and practice , none the less they've been used and abused. Even the losers get lucky sometime , I won't elaborate on whether that's EH or me. I do how ever have a good stock of vintage 6V6's and do appreciate your input and advice. Thanks All !!

EH 6V6 were new to the market at that time right around 2000. I bought a batch and they did work out well, so I was looking forward to a bright future after a decade or two of having only dodgy 6V6's with black glass that rarely functioned well as the only available current product. Alas as the decade wore on subsequent orders brought me EH 6V6 tubes that didn't stand higher voltages well. OK if they had say 325V from plate to cathode but not much beyond that, IOW not much joy in a hot B+ Champ.

FWIW I tried a "dirty trick" in a Champ recently. B+ was up there, around 425V, and the 6V6 red plating. I applied a 470 ohm 5W resistor between rectifier and first filter node. That was enough to drop 25V and the output tube no longer going red. No noticeable change in tone. Of course there was a small reduction in power, but not enough to notice by ear. Seems to have worked OK. We'll see what the future brings with that amp. The output tube in this one was a Philips, the kind you often see with JAN markings on it.

I plan to order in a selection of alternate cathode resistors in the 600 to 900 ohm range so I can adjust Champ - and similar amps' - bias in the more traditional way.

[pdf64]

...FWIW I tried a "dirty trick" in a Champ recently. B+ was up there, around 425V, and the 6V6 red plating. I applied a 470 ohm 5W resistor between rectifier and first filter node. That was enough to drop 25V and the output tube no longer going red. No noticeable change in tone. Of course there was a small reduction in power, but not enough to notice by ear. Seems to have worked OK. We'll see what the future brings with that amp. The output tube in this one was a Philips, the kind you often see with JAN markings on it.

I plan to order in a selection of alternate cathode resistors in the 600 to 900 ohm range so I can adjust Champ - and similar amps' - bias in the more traditional way.

I think the former far less of a bodge than the latter

[Leo_Gnardo]

I think the former far less of a bodge than the latter

Bodge - I LUV English English !!!

Perhaps those resistors are better applied to the hi voltage end of the circuit. To have plenty of power margin I'll order 7 or even 10 watt parts.

[shortcircuit]

EH 6V6 were new to the market at that time right around 2000. I bought a batch and they did work out well, so I was looking forward to a bright future after a decade or two of having only dodgy 6V6's with black glass that rarely functioned well as the only available current product. Alas as the decade wore on subsequent orders brought me EH 6V6 tubes that didn't stand higher voltages well. OK if they had say 325V from plate to cathode but not much beyond that, IOW not much joy in a hot B+ Champ.

FWIW I tried a "dirty trick" in a Champ recently. B+ was up there, around 425V, and the 6V6 red plating. I applied a 470 ohm 5W resistor between rectifier and first filter node. That was enough to drop 25V and the output tube no longer going red. No noticeable change in tone. Of course there was a small reduction in power, but not enough to notice by ear. Seems to have worked OK. We'll see what the future brings with that amp. The output tube in this one was a Philips, the kind you often see with JAN markings on it.

I plan to order in a selection of alternate cathode resistors in the 600 to 900 ohm range so I can adjust Champ - and similar amps' - bias in the more traditional way.

Just to be clear you put the 470 ohm between pin 8 of the 5Y3 and the 40uf connection of the filter cap??

[pdf64]

...Perhaps those resistors are better applied to the hi voltage end of the circuit. To have plenty of power margin I'll order 7 or even 10 watt parts.

Yes, the downside of putting the resistance in the HT rather than in the cathode return is somewhat increased stress, a voltage and power surge at power up.
But that should be fairly limited in a Champ, with a tube rectifier and no standby nonsense, so the HT will ramp up over the course of maybe 20 seconds.

[Leo_Gnardo]

Yes, the downside of putting the resistance in the HT rather than in the cathode return is somewhat increased stress, a voltage and power surge at power up.
But that should be fairly limited in a Champ, with a tube rectifier and no standby nonsense, so the HT will ramp up over the course of maybe 20 seconds.

An advantage is an extra filter cap can be fitted to the circuit with the benefit of knocking power supply hum down to almost nothing. Woohoo! I am so there...

[Leo_Gnardo]

Just to be clear you put the 470 ohm between pin 8 of the 5Y3 and the 40uf connection of the filter cap??

To be honest I forget whether the B+ filter was 40 uF. Some Champs, it's 20. In any case, yes that's the idea. And those with 20uF can always double up or add an extra cap. There's another benefit besides, see above, #41.

[shortcircuit]

To be honest I forget whether the B+ filter was 40 uF. Some Champs, it's 20. In any case, yes that's the idea. And those with 20uF can always double up or add an extra cap. There's another benefit besides, see above, #41.

I'm sorry on the 40uf, I'm applying to a vibro champ ,your talking champ apples/ oranges I get it. As stated above I went with traditional bias method on this VB , and after the cap job, there is no complaint on hum. But I do have another vibro I may try resistance in the HT on , so far I like the traditional biased down Vibro I have. Thanks to you Leo_Gnardo and pdf64 I appreciate the option idea's