5e3 ( VHT Standard 12) voltages question after Sovtek --> JJ rectifier...

[bluesholyman]

Bump up the 250 ohm to 330 ohm if you want it to run a little cooler.
Call it a day, seems sorted as long as it is sounding good.

Agreed about wrapping it up. Going to do a filter cap change in the next week or two once the parts arrive.

Is it any issue to run the tubes at 14w? I have no doubt JJs could handle that, but what about other production 6v6gt's? I suspect these Ruby's will be short lived at that level.

 

[Wally]

Post cap replacement - B+2 F&T cap is measuring 27uF on the meter. B+1 and B+3 are still 16uF for now - both around 17uF on meter.

So, with the JJ 5y3s in there, using the Eurotubes probe, I am getting 310v plate and 35mA current with the black glass Ruby's (120v measured at wall.)

With the Sovtek 5y3, no other changes, I am getting 350v plate and 40mA current, which puts it at 14w dissipation - thats pretty cooking I think. Not seeing any signs of red-plating from the Ruby's, but its black glass.....so....will have to look this evening when its dark.

I am beginning to think this transformer may not be the usual suspect for a 5e3 - its label says dbe-912 hb with a bunch of chinese characters below it, but I cannot find out any info about it. the sovtek seems to provide the juice, much more than the JJ.

I wonder if there were design decisions with regards to that power supply, the sovtek 5y3 and that 470 Ohm bias resistor - it would seem so.

My amp is apparently the Rev C version as shown from this image I got from RobRob's site:

View attachment 998118

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Agreed about wrapping it up. Going to do a filter cap change in the next week or two once the parts arrive.

Is it any issue to run the tubes at 14w? I have no doubt JJs could handle that, but what about other production 6v6gt's? I suspect these Ruby's will be short lived at that level.

This circuit is cathode biased. There is no reason not to run such a circuit at 100% of max plate dissipation at idle. There will be no redplating of a healthy tube. Only the very earliest 6V6s were 12 watt MPD tubes.
in a cathode biased circuit, the idle dissipation is higher than the dissipati9n when proc3ssing signal. A fixed biased situation does just the opposite….the plate dissipation goes up when processing signal. That is why we look to set fixed biased circuit lower at idle.

 

[nickmm]

Only times I've had to reduce the plate dissipation on cathode bias amps is when the stated to eat the commonly available tubes.
My 60's Vox ran really hot and at a time the "new" tubes were not up to it. The old mullards were fine but rattled.

Tube production quality and quality control has improved over the last 20 years

So see what life you are getting from the Rubys.
I generally carry a spare set of JJ 6v6s as back ups for my amps they are pretty rugged.
But I can say new tungsol/mullard 6v6 will red plate easier than the JJs.

 

[Wally]

@Dacious stated that a 5Y3 is a 5Y3 is a 5Y3. If we are talking old stock U.S. made tubes, that could taken as fact. With modern production, that is not so, and @bluesholyman’s experience here proves that. In your position, bluesholyman, I would install a GZ34 just for grins and note the B+. If you get numbers that are similar to the 350Pv you are seeing with that Sovtek 5Y3, then I might think that that Sovtek tube is more like a GZ34l It is handy to have old stock tubes with which to compare. I stopped buying Sovtek rectifiers a long time ago because of tubes that did not yield what a rectifier should yield…and stopped buying other Sovtek tubes not long after that For other reasons. JJ5Y3s and GZ34s compare well with old stock tubes regarding voltage yields, ime.

 

[nickmm]

@Dacious stated that a 5Y3 is a 5Y3 is a 5Y3. If we are talking old stock U.S. made tubes, that could taken as fact. With modern production, that is not so, and @bluesholyman’s experience here proves that. In your position, bluesholyman, I would install a GZ34 just for grins and note the B+. If you get numbers that are similar to the 350Pv you are seeing with that Sovtek 5Y3, then I might think that that Sovtek tube is more like a GZ34l It is handy to have old stock tubes with which to compare. I stopped buying Sovtek rectifiers a long time ago because of tubes that did not yield what a rectifier should yield…and stopped buying other Sovtek tubes not long after that For other reasons. JJ5Y3s and GZ34s compare well with old stock tubes regarding voltage yields, ime.

Yeah hit and miss with new tubes. NOS can get very costly for gigging musicians.


Aren't the original 1960s Fender voltages off due to the USA increasing the wall socket electrons?
I think the OP's amp problems were due to some tech using an internet fix.

 

[Wally]

Yeah hit and miss with new tubes. NOS can get very costly for gigging musicians.


Aren't the original 1960s Fender voltages off due to the USA increasing the wall socket electrons?
I think the OP's amp problems were due to some tech using an internet fix.

Fender was working with 117VAC in mind as early as 1955. See the schematic for the 5E3…the ‘5E’ there indicates the schematic was drawn in 1955. 117VAC.
These days in my area, one can see anything from 123VAC during ‘light demand’ times to 111VAC during times of heavy demand on the grid. That is why I know the source voltage at the wall at the time I am working on an amp.

 

[bluesholyman]

I think the OP's amp problems were due to some tech using an internet fix.

Maybe? The only real fix here I see is the B+2 filter cap - the rest is basically Rev C spec, from what I can tell. I'm just moving it all back towards 5e3 stock spec, but that will probably require replacing the power tranny if I wan't 100% dissipation, or use the Sovtek Rectifier.

These days in my area, one can see anything from 123VAC during ‘light demand’ times to 111VAC during times of heavy demand on the grid.

I run with a variac at home - typically I keep it all around 117v and have seen that suddently climb into the low 120s unexpectedly - voltage varies quite a bit.