I have two JJ 5Y3 tubes. I use them in my 5F11 build. One is putting out around 340 VDC to my plates and the other is putting out around 397 VDC to my plates. Which one is closest to what a 5Y3 is supposed to put out? I currently have the 390 V in it and my 6V6's are running around 24 mA. It sounds pretty good. The other one that puts out 340V is obviously much cooler and I can get 18/19 mA by adjusting the bias pot. It sounds good too. Which one would you run if it were yours? I really don't like the 397V on the plates. I feel that's too hot. Am I wrong?
5Y3 Voltage Delima
- Thread starter DennisM
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AntonyB
TDPRI Member
Have you considered a variac to lower your input voltage hence your power tube plate voltages?
My 70s Champ, like most silverface, has higher plate voltages than its blackface counter part.
A variac to reduce input wall voltage, so that I run the plates at around ~350VDC is indeed more pleasing to my ears.
In the end, your ears decide no?
You can get a useable variac for ~$50... I think people under estimate the value of a variac.
My 70s Champ, like most silverface, has higher plate voltages than its blackface counter part.
A variac to reduce input wall voltage, so that I run the plates at around ~350VDC is indeed more pleasing to my ears.
In the end, your ears decide no?
You can get a useable variac for ~$50... I think people under estimate the value of a variac.
NTC
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What is the ac voltage coming from the power transformer? If you know that, you can look up the graphs in an old 5y3 datasheet and estimate the expected dc voltage. Obviously, one if these is not what it is marked as. It could also be that the lower voltage one has one bad rectifier. I have a 5V4 like that.
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Paul G.
Friend of Leo's
Along as your bias is good, it doreally matter. You say Amp sounds fine either way, so that's your answer.
Ricky D.
Doctor of Teleocity
You could get an NOS 5Y3. That will give you 360 volts. The new production versions are much higher.
Embarrassing as it is, I don't know how to check the AC on the tranny? Which yellow lead to I measure to ground? I know it sounds crazy.
As long as I have your attention, I might ask if I'm measuring the resistance from the primaries on the OP correctly. I'm using the meter set to ohms of course. One side is 215 ohms and the other is 210 ohms. Am I supposed to to read it as resistance or impedance?
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Almost 60VDC difference seems way too much between same type rectifier tubes. The one which rectifies lower voltage is bad. Possibly other diode is inoperative? Or rectifier tube other anode pin is so corrored that it does not conduct properly?
Measure AC and DC voltages over both diodes on both tubes. There is both AC and DC over diodes when they rectify and now when there are two of them you get values which can be used to troubleshoot them.
Measure AC and DC voltages over both diodes on both tubes. There is both AC and DC over diodes when they rectify and now when there are two of them you get values which can be used to troubleshoot them.
NTC
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You are measuring resistance. Impedance uses the same unit as resistance (ohms). Impedance is the apparent resistance of an inductor, capacitor, or a circuit at a given frequency. The meter only reads resistance.
You would measure the ac from each of the two red leads to ground, assuming that is where the center tap is connected. As always, these are dangerous voltages.
TunedupFlat
Tele-Meister
I would say that it depends on the 6v6 you are running. If it were my build I'd be running the 340v 5Y3. The other option is running a 300v-0-300v pt or a 325v-0-325v pt.
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Thanks. That will help a ton. Yes, I am very aware of the voltage dangers, and thanks for reminding me. I stuck the low voltage 5Y3 back in today just for grins. I had to struggle to get 17mA. I had to lower the bias voltage down to -23, and that's about the best I could do to get 17mA, which dropped the plate voltage down to 315. The low voltage one has to be a bad one. After I put in the higher voltage one back in I got the bias V up to -28 and 24mA current. I ended up at about 75% PD. The plates measured 390V which I can deal with because the Electro Harmonics 6V6's are advertised to tolerate 475V.
Thanks for your help and teaching me how to measure the V on the rectifier itself. I'm 65 and still learning
TunedupFlat
Tele-Meister
I forget that modern 5Y3 tend to run hotter than the old glass I use. At the end of the day as long as it works! 
Lowerleftcoast
Poster Extraordinaire
The old 5F11 schematic shows 340 B+. I would probably go with that unless the higher voltage sounded better.
At 340 on the plates, it is running less than 50%MPD. Is there room to bias hotter? Does the sound change with a hotter bias?
At 340 on the plates, it is running less than 50%MPD. Is there room to bias hotter? Does the sound change with a hotter bias?
No room at all. I was down to -23v bias voltage and still barely made it to 17mA. The plates were down to 315V. It would have been ugly to make it to even 20mA. It did sound pretty weak. Much better with the higher V 5Y3. EH 6V6's are advertised to handle 475V so I think the 390V on the plates will be fine. Thanks!
A Variac is designed to be used as a test-only device and not a permanent voltage regulator. ?If you need to drop voltage - which you don't in this case - you should use a voltage regulator - they can be found on Amazon for $100 or so.
First you need to know the voltage coming from the wall outlet! If that is unusually high you DO need a voltage regulator. but don't do anything until you read the whole post
It's not embarrasing - it's flat unsafe. There's no way you should be inside an amp, be checking plate voltages and voltages FROM the rectifier - but not know how how a rectifier works! If you slipped and touched the high voltage coming into..or out of...the rectifier while casually having a finger on the chassis - bye bye Dennis!
It's 1) what determines the voltage the rectifier sends to every applicable part of the amp, and 2) one of THE most critical items you should know about amp safety before even opening a chassis!
No one would be doing you a favor by telling you how to test for it. Seriously - you should close the amp and take or ship it to a qualified tech, and study basic electronics AND electronics safety before working on an an amp again.
This isn't meant to be mean. It's meant to ensure you have proper knowledge about amplifier operation and safety so you don't injure - or kill- yourself.
Sorry, but you are NOT at all aware (much less "very" aware) of the voltage dangers if you did not know how to determine voltage coming INTO the rectifier tube!
This is NOT something you learn while building or working on an amp - it's a vital part of safety awareness you need to know BEFORE doing either.
NTC
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Thanks. That will help a ton. Yes, I am very aware of the voltage dangers, and thanks for reminding me. I stuck the low voltage 5Y3 back in today just for grins. I had to struggle to get 17mA. I had to lower the bias voltage down to -23, and that's about the best I could do to get 17mA, which dropped the plate voltage down to 315. The low voltage one has to be a bad one. After I put in the higher voltage one back in I got the bias V up to -28 and 24mA current. I ended up at about 75% PD. The plates measured 390V which I can deal with because the Electro Harmonics 6V6's are advertised to tolerate 475V.
Thanks for your help and teaching me how to measure the V on the rectifier itself. I'm 65 and still learning
Something is not right here though. Two things specifically. First, there should not be much difference, certainly not that much difference, between those JJ 5Y3s. The JJs drop about as much or even more than NOS 5Y3GTs. 340ish volts sounds more correct. What power transformer do you have?
Second, your 6V6s should be cooking at -23 on the grids, even at around 315V on the plates. So again, something doesn't seem right here. How old are your 6V6s? What were your initial voltage and bias numbers when you completed the amp? How exactly are you measuring the plate (or cathode) current?
[email protected]
TDPRI Member
Dennis,
Max voltage on a 6V6 is like 330V... but fender really never did that. They were always high and that led to changes in the design of the 6V6. Your current is a little low as typically 6V6 (at least mine) are biased to the full 14W. So V/I = W with the 390 (which will come down) you could closer to 30ma.
I am a little surprised at the variation of voltage. I use them in my amps and they are always pretty close. If you have a tube tester check them both out.
Thanks,
Gordon
It is not advisable to bias to 100% of MPD in a fixed biased, push/pull circuit. It can be done, but tube life will suffer. In fixed biased, the plate dissipation increases when signal is being processed. That is why most would not bias such a circuit at 100% of MPD at idle.
@Wally I would also be willing to bet that even JJs running at 100% in fixed bias will drift into thermal runaway.
Hot tubes will bias themselves hotter. Cathode bias helps to prevent that from happening, fixed bias does not.
Hot tubes will bias themselves hotter. Cathode bias helps to prevent that from happening, fixed bias does not.
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