5Y3 Rectifier Tube Question

[tele-martini]

Can someone help me get thru this confusion on rectifier tubes. I have read that a modern Sovetek 5Y3 rec tube is not a true 5Y3 and actually increases voltage.
1.)Are 5U4 tubes and 5Y3 interchangable or would the amp need to be re-biased in a non fixed bias amp.

2.) Are 5U4 tubes only available in NOS.

3.) Are there any other rectifier type tubes commonly used, I thought I'd read posts where someone uses a 5V4.

Thanks,
Gene

[Brent Hutto]

I've been studying up on rectifiers lately and the 5Y3 has about as much internal resistance as any of the similar rectifiers out there. When the amp is pulling a lot of current (where "a lot" for a 5Y3 is anything more than say 30, 40, 50 milliamperes) the voltage coming out of a tube rectifier drops. The number you commonly see quoted for a 5Y3 is about 50V at 125mA which equates to a series resistance of 400 ohms. By comparison, I believe a 5U4 is more in the under 200 ohms range so call it half the voltage drop at the same load.

My amp draws something like 75mA all told (one power tube, one rectifier tube) with a 6L6 and maybe 55mA with a 6V6 so in that case the output voltage under load if I swapped in a 5U4 would be about 10-15V higher than with the specified 5Y3. Amps with two power tubes the difference scales accordingly.

But again, almost any substitute for a 5Y3 will result in at least slightly higher voltage under load. You just need to judge whether your amp will sound good running at, say, 400V instead of 380V or whatever it is. And of course make sure the power tubes aren't already running over their maximum plate voltage and check the bias after the swap.

But everyone does report that the Sovtek 5Y3 has considerably lower than 400 ohms of effective source resistance. Why not just put an NOS 5Y3 in there? They are widely available for $20-ish and if you shop around probably less than that. The build quality of the vast majority of NOS rectifiers is better than that of a new Eastern European one anyways. If you really want overkill, you can get a Bendix 6106 for about $40 that will be nigh indestructable and has a slow-warmup indirectly heated cathode to boot (however, it has slightly lower voltage drop than a normal 5Y3 too).

[EMan]

Great post Brent. I'll bet there's a plate curve plot out there somewhere for the Sovetek 5y3, that will answer the question.

As far as 5Y3's go, AES sells them (NOS) for less than $20. The 5Y3GT in my brown Princeton has been in there since 1976..I'd say it's a good 'investment' .. :-)

[Brent Hutto]

Yeah, if it were a tire I don't think you'd get much of a prorated warranty out of it at this point...

[tele-martini]

Originally Posted by Brent Hutto

I've been studying up on rectifiers lately and the 5Y3 has about as much internal resistance as any of the similar rectifiers out there. When the amp is pulling a lot of current (where "a lot" for a 5Y3 is anything more than say 30, 40, 50 milliamperes) the voltage coming out of a tube rectifier drops. The number you commonly see quoted for a 5Y3 is about 50V at 125mA which equates to a series resistance of 400 ohms. By comparison, I believe a 5U4 is more in the under 200 ohms range so call it half the voltage drop at the same load.

My amp draws something like 75mA all told (one power tube, one rectifier tube) with a 6L6 and maybe 55mA with a 6V6 so in that case the output voltage under load if I swapped in a 5U4 would be about 10-15V higher than with the specified 5Y3. Amps with two power tubes the difference scales accordingly.

But again, almost any substitute for a 5Y3 will result in at least slightly higher voltage under load. You just need to judge whether your amp will sound good running at, say, 400V instead of 380V or whatever it is. And of course make sure the power tubes aren't already running over their maximum plate voltage and check the bias after the swap.

But everyone does report that the Sovtek 5Y3 has considerably lower than 400 ohms of effective source resistance. Why not just put an NOS 5Y3 in there? They are widely available for $20-ish and if you shop around probably less than that. The build quality of the vast majority of NOS rectifiers is better than that of a new Eastern European one anyways. If you really want overkill, you can get a Bendix 6106 for about $40 that will be nigh indestructable and has a slow-warmup indirectly heated cathode to boot (however, it has slightly lower voltage drop than a normal 5Y3 too).

Great info Brent ,thankyou for taking the time to post!!

Originally Posted by EMan

Great post Brent. I'll bet there's a plate curve plot out there somewhere for the Sovetek 5y3, that will answer the question.

As far as 5Y3's go, AES sells them (NOS) for less than $20. The 5Y3GT in my brown Princeton has been in there since 1976..I'd say it's a good 'investment' .. :-)

Sounds like a good plan Eman. The question came to mind yesterday when I rec'd a 76 Princeton Reverb w/5U4 RCA rec tube and the 5E3 kit I recently built had the Sovetek 5Y3 rec tube supplied.

[ce24]

Tele-Matini I put a 5V4 in my 5E3 and it's working fine....seems to have more clean headroom but that's just ears opinion..

Cheers
ce24

[Scott S]

Originally Posted by tele-martini

1.)Are 5U4 tubes and 5Y3 interchangable or would the amp need to be re-biased in a non fixed bias amp.

Be careful swapping them. A 5U4 requires a 5V, 3A (15W) filament tap, and most of the smaller amps which originally used 5Y3's only have a 5V, 2A (10W) tap. That extra 5W of current draw could make your PT toasty.

And if you run a 5Y3 in an amp that was designed for a 5U4, the amp's B+ current draw could make the 5Y3 arc.

- Scot

[tele-martini]

Originally Posted by ce24

Tele-Matini I put a 5V4 in my 5E3 and it's working fine....seems to have more clean headroom but that's just ears opinion..

Cheers
ce24

Have you checked or compared the B+ voltage since you swapped tubes?

After checking out a few of my usual tube sources I see there are many NOS 5Y3's available for around the $20 price. I think I'll order a couple and see how they affect the B+ voltage in my 5E3 clone and post results.
Thanks,

Gene

[EMan]

Keep in mind as well, that there is an 'idea' input filter for each application, and different rectifier tubes have limitations of how much capacitance they can drive. I think folks forget that it only takes 50uF of filtering to run a 100W Twin.

[stratavox]

...I've used Weber's Copper Caps in all my amps and builds with no issues, and no draw on the P/T...

[marshman]

If you need rectifiers, I have two words for you:

1) Ham

2) Fest

I pick up 3 or 4 every year for less than 3 bucks a piece, both 5Y3 and 5UGBs, though I haven't seen a 5AR4/GZ34 in ages...I guess even the old ham nuts have seen them goin' for $50 on ebay...

[EMan]

Marshman - absolutely right. I have a friend that's an old ham'r, and he's always scoring good ol' tubes at his local 'fests.

[austintele]

Originally Posted by tele-martini

Have you checked or compared the B+ voltage since you swapped tubes?

After checking out a few of my usual tube sources I see there are many NOS 5Y3's available for around the $20 price. I think I'll order a couple and see how they affect the B+ voltage in my 5E3 clone and post results.
Thanks,

Gene

I have a 5V4 in my tweed deluxe copy and it measures 395 volts on pin 3. I do run a 5y3 in my 58 tweed champ just because that's what the amp has been "seeing" for the last 50 years and why rock the boat