Happy Vibro Champ

[shortcircuit]

using actual voltage across pin 3 to 8 is 391vdc , I went pin 3 to grnd to get 418vdc. I still agree 20's are hot, I will bias down and see if I turn into claptone . going back to post 6 & 8 , I'll try these and check any difference in dissipation, just for a test. I'll be back
[ATTACH=CONFIG]48642[/ATTACH]

Here is the 5y3 results comparing to Sovtek v drop 26.80vdc , all v drop are across cath resistor , test before re-cap
GE Filtron V drop 25.20vdc V across pins 3 to 8 370vdc
Sylvania V drop 25.01vdc V across pins 3 to 8 368vdc
Amperex V drop 25.48vdc V across pins 3 to 8 372vdc
Jan Phillips 5y3WGTA V drop 24.77vdc V across pins 3 to 8 363vdc
from post #6 I'll have to start with 25/50v that's what I've got
A note remember this has the champ champ mod , the schematic from my original post is stock
in the champ champ instructions the mod will raise the gain a whole bunch , change a lazy circuit to a hot one
THANKS TO ALL , I shall return

[shortcircuit]

Here is the 5y3 results comparing to Sovtek v drop 26.80vdc , all v drop are across cath resistor , test before re-cap
GE Filtron V drop 25.20vdc V across pins 3 to 8 370vdc
Sylvania V drop 25.01vdc V across pins 3 to 8 368vdc
Amperex V drop 25.48vdc V across pins 3 to 8 372vdc
Jan Phillips 5y3WGTA V drop 24.77vdc V across pins 3 to 8 363vdc
from post #6 I'll have to start with 25/50v that's what I've got
A note remember this has the champ champ mod , the schematic from my original post is stock
in the champ champ instructions the mod will raise the gain a whole bunch , change a lazy circuit to a hot one
THANKS TO ALL , I shall return

Took a step farther , pulled the drawer on another 79 vibro champ , this one is stock
cath R = 463ohms
V drop across R = 25.42vdc
V across pins 3 to 8 = 402vdc
do the math , comes out with that same .055ma , 20.71 dissipation , so as Enzo and others stated hot seems to be the norm
I'm still going to do some cath R swaps just for curiosity , hopefully I'll have better results than the cat.

[mac dillard]

Sometimes you end up chasing your tail trying to get the dissipation down. Up the cathode resistor and the anode voltage goes up.

[g1]

You are talking about the V drop across the cathode resistor, I just want to make sure there is no confusion about the V drop across the 5Y3 rectifier tube that the others were speaking of.
Doing the math, you have about 20 to 25V less plate voltage with the NOS 5Y3's compared to the Sovtek. So the NOS tubes are dropping approx. 20VDC more across themselves.
This is why people avoid the Sovtek 5Y3's, they are not a true 5Y3 and end up jacking up your B+ supply to sometimes dangerous levels.

[pdf64]

With vintage amps in North America, the 1st step would seem to be to check the actual heater voltage. There's a fair chance that the PT was designed for a mains nominal of 110 or 115V, and you may be feeding it 125V from your wall outlet. So comparing the actual measured loaded heater voltage to the nominal 6.3V should reveal that.
I've read reports that even well into the 60s, using the above procedure, some 'student' level Fender amps still seemed to have PTs designed for 110V (rather than the 117V noted on the layouts of stage level amps), and hence run crazy hot today. These would seem to be a good candidates for a mains bucker.
http://schems.com/schematicheaven.ne...b165_schem.pdf

With cathode biased amps, if the issue really is just due to excessive HT, as per post #118 below, it seems counterproductive / wrongheaded to mess with the bias. Surely it's more effective to address the issue directly and add some resistance in series with the rectifier so as to bring the HT down to more reasonable level, ie one that results in a sensible idle plate dissipation.

[Justin Thomas]

Sovtek 5Y3 = a Sovtek GZ34 that got a D- in QC...

Or so I've heard. Like many things Sovtek, they're not a "true match," like the EL84, 5881WXT, etc. It's "close enough to work in most circuits," but if that circuit is already borderline, well then...

Justin

Edit: not to say they're bad tubes, because though some may say they don't "sound good," those 5881s are dang-near indestructible, and the EL84s take a good bit of punishment, too...

[shortcircuit]

You are talking about the V drop across the cathode resistor, I just want to make sure there is no confusion about the V drop across the 5Y3 rectifier tube that the others were speaking of.
Doing the math, you have about 20 to 25V less plate voltage with the NOS 5Y3's compared to the Sovtek. So the NOS tubes are dropping approx. 20VDC more across themselves.
This is why people avoid the Sovtek 5Y3's, they are not a true 5Y3 and end up jacking up your B+ supply to sometimes dangerous levels.

Yes confusion , I did not measure across the rectifier , I had tunnel vision focused on Cathode resistor drop ,and dissipation to the 6v6 . I'm still a basics 101 guy (almost)

[The Dude]

Best is to measure B+ and compare tube to tube. Use the one with the lowest B+.

[shortcircuit]

Best is to measure B+ and compare tube to tube. Use the one with the lowest B+.

Thanks appreciate your input as always, did play with cath resistor , it took a 825ohm to get a 31.5 drop , 400v across pins 3 & 8 .038ma to get a 14v dissipation , and it did raise pin 5 to 8 from 26.62vdc to 31.50vdc

[g1]

How about with than JAN Philips 5Y3 in there now?

[The Dude]

Not a big deal, because we know what you mean, but it's not .038ma. It's either .038A or 38mA. Just pointing it out. It might be confusing in some other scenario.

[shortcircuit]

How about with than JAN Philips 5Y3 in there now?

cathode resistor drop 30.55vdc , across pins 3 & 8 on 6V6 386vdc , .037a(thanks Dude) , dissipation 13.15vdc , pins 5 to 8 on 6v6 29.75vdc

[mozz]

Highest i am seeing 20.6w 147%, lowest 17.6w 125%. That is both with the 483 ohm resistor. Put the Phillips 5y3 in, run a JJ 6V6S, you should be set.

I mentioned not going to high with the cathode resistor due to building and reading about the 18w (Marshall) on said site. They had said you go too high and you lose the tone. I have not experimented with that , yet. Picked up 60 pieces of 6p14p-k early 70's date coded i have to torture test. Maybe my old Sony video camera will show redplating better than i can see.

[g1]

I had to go up to 1K on the cathode of a Tweed Champ and the owner is nuts about the tone.

[Chuck H]

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.