5Y3 Voltage Delima

[Bloozestringer]

I don't know about new 5Y3's, but my old ones tend to drop 40-50V.

Silverface is correct. If you don't know what you're doing and you're concerned I would have someone who does check things out for you. Safety first.

 

[King Fan]

OP, did anyone ever tell you how to measure the HT voltage coming into your rectifier? Google "5Y3 pinout images" and you'll get something like this:

We measure with all tubes in, of course. Set meter to AC, selecting the right range if needed. Yellows you mentioned are heater voltage, 5 VAC pin to pin. Worth checking, but here you want the high tension (HT) high voltage leads, those are pin 4 and 6. Typical small-amp PTs put out 275 to 350VAC on each HT secondary, making total across the pins of 550 to 700, so it is way *easier on your meter* to measure *pin to chassis on each pin.* Even 275-350 is still very high, so all safety precautions apply -- mini-grabber probes are a big safety upgrade, so you can clip in your probes, then turn on the amp. But if you're going to measure voltages, the same safety precautions apply everywhere.

A logician would have another way to decide which of your JJs 5Y3s is funky -- if you buy a third one, two of them will likely be fairly close. JJs are in the correct 5Y3 ballpark though some NOS may drop a bit more voltage; if you came across a Sovtek 5Y3, note they drop less voltage than a 5Y3 should.

 

[V52S]

Here's the data sheet for the 5Y3GT.
Hope it helps.
-v-

 

[DennisM]

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?

Hi and thanks! I am going to leave it with the 390V tube. All of the voltages are more in line with what they are supposed to be. The old original schematics do show 340V at B+, but I'm considering that when that was done the wall AC was running 110V. My wall AC varies between 119/123V. That equates to between 30 and 40 VDC higher than the original. As far as voltage on 6V6's, my PRRI is running at 427VDC, and that was what the original 1965 schematic is showing when wall AC was 117VAC.

As far as plate current, I'm dividing the V drop on the primaries of the OPT by the resistance of the same primary leads.

It sounds killer with the higher 5Y3. Thanks!

 

[Phrygian77]

Hi and thanks! I am going to leave it with the 390V tube. All of the voltages are more in line with what they are supposed to be. The old original schematics do show 340V at B+, but I'm considering that when that was done the wall AC was running 110V. My wall AC varies between 119/123V. That equates to between 30 and 40 VDC higher than the original. As far as voltage on 6V6's, my PRRI is running at 427VDC, and that was what the original 1965 schematic is showing when wall AC was 117VAC.

As far as plate current, I'm dividing the V drop on the primaries of the OPT by the resistance of the same primary leads.

It sounds killer with the higher 5Y3. Thanks!

You're not listening.

Your 6V6s, again, based on the numbers you are providing:

-23V grids 17mA at 315V. That should be closer to 30mA with those voltages!
-28V grids 24mA at 390V. That should be closer to 40mA!

Something is wrong! You either have some extremely cold 6V6s, or they are nearly cathode depleted.

You're not helping me help you either by not answering my questions about the power transformer, or your original voltage and bias numbers with those tubes.

Do whatever you want to do, but I think you're ignoring problems, and they aren't just going to go away.

 

[DennisM]

You're not listening.

Your 6V6s, again, based on the numbers you are providing:

-23V grids 17mA at 315V. That should be closer to 30mA with those voltages!
-28V grids 24mA at 390V. That should be closer to 40mA!

Something is wrong! You either have some extremely cold 6V6s, or they are nearly cathode depleted.

You're not helping me help you either by not answering my questions about the power transformer, or your original voltage and bias numbers with those tubes.

Do whatever you want to do, but I think you're ignoring problems, and they aren't just going to go away.

Really not trying to piss anyone off. I bought the transformer from AES back in 2017. They sold trannys by unbranded ClassicTone I believe. Classictone went out of business so I can't find the exact tranny. I bought the one for a 5E3 along with the OP tranny also for a 5e3, which is what mojotone uses in their kits for a 5F11. I believe they are rated at 384-0-384 with a 50V bias tap. 5VAC.

This amp started as a 5e3 deluxe back in 2017 but it was too much amp for me so I converted it to a 5f11 with the same chassis and parts. I had to do some PTP wiring for the tremolo and bias circuit. It's been a while but I think it was putting out 383 VDC on the plates. The 5e3 was cathode bias and I don't remember what the bias was at that time.

I learned from Uncle Doug's videos about setting the bias by measuring the resistance of the primary leads of the OPT, then reading the voltage drop from the same leads. Ohms law. I=E/R. VD=5.10VDC divided by the primary resistance=215 ohms = .0237 amps =23.7 mA. The other lead is 210 ohms and VD is 4.41VDC which =.0214 amps=21.4mA. I installed a 10K bias pot so I could fine tune the resistance to achieve the plate current I wanted. That's the way I do it as I learned from him.

I don't claim to be an amp tech, that's why I ask questions. I've learned a lot by asking.

I know all about safety. I know what not to touch and I know this voltage can be lethal. I drain the caps when the amp is off and unplugged. I use the meter on the caps to make double sure they are drained. I practice the one hand in the pocket technique while working in there. I use the top of the chassis bolts as my grounding point with my probe so I only have one hand at a time in there....except to measure the voltage drop.

 

[Phrygian77]

Really not trying to piss anyone off. I bought the transformer from AES back in 2017. They sold trannys by unbranded ClassicTone I believe. Classictone went out of business so I can't find the exact tranny. I bought the one for a 5E3 along with the OP tranny also for a 5e3, which is what mojotone uses in their kits for a 5F11. I believe they are rated at 384-0-384 with a 50V bias tap. 5VAC.

This amp started as a 5e3 deluxe back in 2017 but it was too much amp for me so I converted it to a 5f11 with the same chassis and parts. I had to do some PTP wiring for the tremolo and bias circuit. It's been a while but I think it was putting out 383 VDC on the plates. The 5e3 was cathode bias and I don't remember what the bias was at that time.

Okay, this is helpful information, and none of it was in mentioned in your original post. A 5F11 would normally have a Champ / Princeton Reverb size power transformer. You've got a Deluxe size power transformer. Given that, then I think that the lower B+ numbers with one of the 5Y3s are suspicious, rather than the other way around.

 

[TunedupFlat]

Uncle Doug's work on YouTube is a treasure trove of information. If it were me, I still would do a pt in the amp that was lower vac if I was able to. But with it running as it is, I'd have a tough time justifying the extra cost.

Would love to see a gut shot of your amp!

 

[DennisM]

Uncle Doug's work on YouTube is a treasure trove of information. If it were me, I still would do a pt in the amp that was lower vac if I was able to. But with it running as it is, I'd have a tough time justifying the extra cost.

Would love to see a gut shot of your amp!

Yes he is!! I've learned a bunch from him. I'll get some gut shots today sometime. Thanks!

 

[warchol]

If you can't hear enough difference in tone to decide which to use,
I would go with the lower voltage for two reasons:

Lower voltage stress on all the parts in the amp = better reliability

Lower voltage on the power tubes = Earlier breakup at lower volumes, which I happen to like

Just make sure to bias the wattage dissipation within the rating of the tubes you are using...

YMMV

 

[Wally]

24ma at 390Pv is about 67% of max plate dissipation…which is right where I would want it for a 5F11 fixed biased circuit. Ommv.

 

[DennisM]

24ma at 390Pv is about 67% of max plate dissipation…which is right where I would want it for a 5F11 fixed biased circuit. Ommv.

I had it figured at around 77% based on 12 watts. I guess nowadays we base it on 14 watts? Either way it's pretty good and it sounds wonderful. Thanks Wally!

 

[DennisM]

If you can't hear enough difference in tone to decide which to use,
I would go with the lower voltage for two reasons:

Lower voltage stress on all the parts in the amp = better reliability

Lower voltage on the power tubes = Earlier breakup at lower volumes, which I happen to like

Just make sure to bias the wattage dissipation within the rating of the tubes you are using...

YMMV

After putting back in the weaker tube and running at 315V and around 17mA, I like it much better with the higher tube at 390V and 24mA. I'm going to leave it there. The tremolo is good and strong and the amp runs totally quiet...can't even tell it's on.

 

[Wally]

I had it figured at around 77% based on 12 watts. I guess nowadays we base it on 14 watts? Either way it's pretty good and it sounds wonderful. Thanks Wally!

6V6s have had a MPD of 14 watts for about 60 years now, iirc. Only the older spec sheets stipulate 12 watts, ime.

 

[DennisM]

Here ya go @TunedupFlat. Since is was a deluxe I had to rearrange pots/knobs. I elected to go with just two inputs. I use only #1 anyway. Try not to laugh...it works. It was a challenge using the deluxe tag board. Point to point in some spots in a very unorthodox manner. I built and covered the cab myself. 3/4 pine throughout. I had to make an adaptor from 12" to 10" for the speaker.

 

[TunedupFlat]

I'm definitely not going to laugh, as I did a PTP 5e3 about 10 years ago and that looked like a total rats nest. At the end of the day as long as the PTP stuff has a good mechanical connection it will hold.

I like it!