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 Post subject: Question about voltages; 5v4GA tube
PostPosted: Mar Fri 02, 2018 3:04 pm 
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Location: Bristol, Rhode Island
Hi,

I just built a push pull 6v6 amplifier out of some transformers i have laying around. B+ voltage is around 320V; about 40 or so volts south of where I would like it to be. I'm running a 5Y3 rectifier but would like to swap it out for something with a smaller voltage drop. But I can't use a 5U4 because the 5V winding is 2a, and using a solid state diode bridge (already tried) puts the voltages too high and makes the delivery too stiff.
So I am thinking about trying a 5v4ga, which looks like it should give me just about the right B+.
My question is this: Ratings for the 5V4 specify a first filter cap of 10uf max. The circuit currently has a 22uf cap in the first spot, but I could reduce it to 16 (10 might be too low).
To those of you who may have used a 5V4ga before, do you think the tube can handle a 16uf cap in the first slot? I don't want to fry the rectifier.

And if I did decided to try a 10uf anyway, would I then want to up the capacitance of the second cap (currently also 22) to account?

Thanks!


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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Fri 02, 2018 3:47 pm 
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If the specs says 10mfd max, that's the spec.
They specify that value for a reason.

Use 10mfd and increase the second filter cap to maybe 47mfd.

If the B+ ends up too low, reduce the resistance between the filter caps.

The PSuD II program from Duncan Amps will tell you everything about any PS design.
http://www.duncanamps.com

- Leigh

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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Fri 02, 2018 5:45 pm 
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Location: Bristol, Rhode Island
Yep, I suspected this would be the answer.
I mostly asked because in most of the designs for these amps that I build, specs for many components (particularly) tubes are often 20, 30 or 40 percent higher than the max allowed plate and other ratings for those tubes. Just wondering if anyone had real-world experience as to whether the 5V4 can go higher with no ill effects.
Thanks for the suggestion, any way. I'll start off by dropping the first to 10 and upping the second to 47 or so, and will adjust power resistors accordingly based on where the voltages end up.
Have a great day. Thanks!


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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Fri 02, 2018 5:55 pm 
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Diverted wrote:
I mostly asked because in most of the designs for these amps that I build, specs for many components (particularly) tubes are often 20, 30 or 40 percent higher than the max allowed plate and other ratings for those tubes.

That's called Aduiophile amplifier design.

There is absolutely no justification for exceeding tube ratings.

- Leigh

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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Fri 02, 2018 5:58 pm 
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I'm missing something....why not a couple of 1n4007s or similar?

Since you are using available parts, another option is a doubler. I just finished a Fisher 400 (tube) that uses a full-wave s/s doubler to get the ~420 volts for the output tubes. (Before I tweaked it, a total of almost 200 mA just for the 4 output tubes)
I have never seen so many millifarads of filter caps in a receiver......

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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Fri 02, 2018 6:02 pm 
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Leigh wrote:
Diverted wrote:
I mostly asked because in most of the designs for these amps that I build, specs for many components (particularly) tubes are often 20, 30 or 40 percent higher than the max allowed plate and other ratings for those tubes.

That's called Aduiophile amplifier design.

There is absolutely no justification for exceeding tube ratings.

- Leigh

Sure there is......Aduiophile with more money than brains finds that special sound they have been seeking. While we're on this side road, which is worse: Audiophools or Guitar players?

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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Fri 02, 2018 6:09 pm 
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Leigh wrote:
Diverted wrote:
I mostly asked because in most of the designs for these amps that I build, specs for many components (particularly) tubes are often 20, 30 or 40 percent higher than the max allowed plate and other ratings for those tubes.

That's called Aduiophile amplifier design.

There is absolutely no justification for exceeding tube ratings.

- Leigh

Well, it's worked for Leo Fender for 60 years. Take a look at the voltages on the output tubes on many popular early models. These amps have stood the test of time and regularly run for many years without issue. I'm not going to argue with that.

For instance, 315v is max spec'd voltage on a 6V6GT. Most, if not all, of the amps Fender and other 60s-present makers see plate voltages closer to 360 or 370, some approach 400 or more. They bias them conservatively, and the tubes stay happy.

Is Fender an "Aduiophile?" Millions of these amps out there.


Last edited by Diverted on Mar Fri 02, 2018 6:15 pm, edited 1 time in total.

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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Fri 02, 2018 6:12 pm 
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Location: Bristol, Rhode Island
pixellany wrote:
I'm missing something....why not a couple of 1n4007s or similar?

Since you are using available parts, another option is a doubler. I just finished a Fisher 400 (tube) that uses a full-wave s/s doubler to get the ~420 volts for the output tubes. (Before I tweaked it, a total of almost 200 mA just for the 4 output tubes)
I have never seen so many millifarads of filter caps in a receiver......


When I first fired it up with the 5Y3 and saw the low voltages, I switched to 1N4007s. But I found that the resulting sound wasn't what I wanted. No tube "sag" with that solid state voltages and as a result, the amp performed nothing like what it hsould (it is a Fender 5E3 circuit). On the correct circuit dialing overdrive distortion is relatively easy, you start hearing it halfway up the volume setting.
With the solid state voltage the amp was punchier and super clean. No overdrive, even with the volume maxed. If I was going for a super clean, crisp tone it would have been perfect, but was looking for that vintage fuzz tone the amp is famous (and loved) for.

Thanks!


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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Fri 02, 2018 6:14 pm 
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Max plate voltage ratings for 6V6 & GT versions is 315v, for a GTA it's 350v...

The Audiophoolery practice of overrating tubes apparently stems from computer overclocking that should include additional cooling... I doubt heat is seldom considered for the tubes being abused...

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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Fri 02, 2018 6:18 pm 
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Having no experience in reducing the performance of something to make it "sound better", I hereby defer......

But, if you need "sag", how about a series resistor?

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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Fri 02, 2018 6:26 pm 
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Location: Bristol, Rhode Island
pixellany wrote:
Having no experience in reducing the performance of something to make it "sound better", I hereby defer......

But, if you need "sag", how about a series resistor?

Didn't really helped too much. When I had the diodes in place with B+ way too high I added a resistor to the HV center tap to ground. It improved the sonics but not as much as I hoped it would.
So just looking for every possible alternative and solution before I settle on one.
Thanks all for the help.


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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Sat 03, 2018 4:55 pm 
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Congrats on your build so far. It sounds like you are compensating for an undersized power transformer, but I think you know that.
You could eventually put solid state diodes in there on a switch. I did that for a buddy once, two hefty diodes in series. 5E3 circuit with a 5Y3 tube.

Oh, BTW, if the 5V3 tube drops less voltage, you will see a diminished effect from it. The sag in the B+ is more pronounced when it is 30+ volts, just saying.
I guess you could have 2 rectifier sockets and switch between them. :D

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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Sun 04, 2018 12:24 am 
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westcoastjohn wrote:
I guess you could have 2 rectifier sockets and switch between them. :D


Thanks Westcoast John. That's a very cool thought. Maybe I'll pick up a 5AR4 and drop it in ... I'd have to move some stuff around on the old reclaimed chassis I'm using but I do have an extra socket I could use. That'd be a nice feature.
Tweaked the amp a bit to accommodate the 5V4. Went with two 22ufs in series for the first cap and 39uf for the second. Didn't have to tweak the power resistors .. power rail voltages are close enough to where they should be. Just needed to up the cathode resistor from 250 to 330 ohms as it was running pretty hot. Amp's now dissipating at about 95 percent, transformer's cool, all good so far! Tone much, much better and breakup starts more or less where it should be. Sounds very good. Dead quiet at idle too, pretty happy about that. Haven't played with it too much because we lost power in the storm but I'll get back to it later this weekend.


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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Sun 04, 2018 1:10 am 
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You survived the storm and are still above the high tide line? All good. 8)

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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Sun 04, 2018 1:31 am 
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westcoastjohn wrote:
You survived the storm and are still above the high tide line? All good. 8)


House is about 100 yards from the bay, but luckily uphill a good 30 feet. Also, it's built on sharp sloping ledge, no full basement, so no flooding ever. Lucky!


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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Mon 05, 2018 8:28 pm 
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35Z5 wrote:
Max plate voltage ratings for 6V6 & GT versions is 315v, for a GTA it's 350v...



Here is one of Fender's most famous and respected designs ... note that this amp sees 415V on the 6V6GT plates. No 6V6GTA in sight. If it was a tube killer it would have gotten an entirely different reputation than the one it does.

http://schematicheaven.net/fenderamps/d ... _schem.pdf

I appreciate all the help here and would be nowhere near where I am today without the help of all of you.
Still, sometimes I wonder why there is this "us vs them" and holier than thou attitude between radio guys here and so-called "audiophools."
I can understand sites like this ragging on people who sell $5,000 RCA cables (I make fun of them too). But some of the posts in this thread, which rigidly quote tube ratings as scripture, seem a little extreme. It's very obvious when one looks that these ratings are often exceeded, in many different circuits, with no ill effects. Given this, why not question original assumptions about the validity of max ratings? Doing so doesn't make one a "phool." I may not know much but I do know that many amplifier designs are just fine even though those gospel specs are often exceeded by 20 or 30 percent.
Leigh wrote somewhere in this thread that "there is absolutely no justification for exceeding tube ratings." I just don't see why.


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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Mon 05, 2018 9:32 pm 
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There are some people that won't drive faster than the speed limit. Progress is made by pushing the envelope. Limits are made to be exceeded :)

Dave


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 Post subject: Re: Question about voltages; 5v4GA tube
PostPosted: Mar Wed 07, 2018 3:30 am 
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Different strokes. Do you want your tubes to last for ever, or do you want them to shake the rafters and make girls WTP? :lol:

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