Choices in rectifier tubes for VTA?

LEVLHED: Posts: 21
Join date: 2009-10-26

Post n°1

Choices in rectifier tubes for VTA?

by LEVLHED on Wed Nov 18, 2009 8:31 am

I've been throughly enjoying my VTA ST-70, recently picked up a Dared SL-2000A preamp and it seems like the perfect match. Now I'm looking into trying some different tubes.

Since I've already got some Mullard input tubes order and I've got driver tubes on a few Christmas lists ( Smile

) I was wondering what peoples experiences are with different rectifier tubes for this unit.
Mine currently has a Sylvania. I have no idea how it compares to the myriad of other choices out there.

Bob Latino

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Post n°2

Re: Choices in rectifier tubes for VTA?

by Bob Latino on Wed Nov 18, 2009 9:14 am

LEVLHED wrote:I've been throughly enjoying my VTA ST-70, recently picked up a Dared SL-2000A preamp and it seems like the perfect match. Now I'm looking into trying some different tubes.

Since I've already got some Mullard input tubes order and I've got driver tubes on a few Christmas lists () I was wondering what peoples experiences are with different rectifier tubes for this unit.
Mine currently has a Sylvania. I have no idea how it compares to the myriad of other choices out there.

Hi,

Probably the best GZ34 rectifier tube ever made was the Mullard GZ34 but they are expensive at $50+ (used) and $150 or so NOS. Your USA "Sylvania" could be a Mullard. Look on the bottom of the center pin. If there is a little hole in there it was probably made by Mullard. Your Sylvania could also be an older USA production tube which were usually very well made. Your Sylvania is probably a better tube than any GZ34 produced today.

Of the current choices out there for newer production tubes there is the JJ, the Sovtek and the Ruby GZ34. Of the three tubes mentioned IMHO the Ruby is the best of the bunch and seems to last longer than the JJ or Sovtek tubes in an ST-70. A friend of mine mentioned to me that a lot of guitar players like the Ruby GZ34 in their tube guitar amps.

Bob

LEVLHED

LEVLHED: Posts: 21
Join date: 2009-10-26

Post n°3

Re: Choices in rectifier tubes for VTA?

by LEVLHED on Wed Nov 18, 2009 10:00 am

I'll check the center pin when I get home, thanks for the tip.
Though I could also ask, have you sold any completed kits recently with a Mullard? Seeing as how I just bought this from a guy in Puerto Rico who'd recently bought it from you as a completed kit!
I'm certain he did not replace any tubes, they are all the same ones as when he bought it.

Bob Latino

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Post n°4

Re: Choices in rectifier tubes for VTA?

by Bob Latino on Wed Nov 18, 2009 10:17 am

LEVLHED wrote:I'll check the center pin when I get home, thanks for the tip.
Though I could also ask, have you sold any completed kits recently with a Mullard? Seeing as how I just bought this from a guy in Puerto Rico who'd recently bought it from you as a completed kit!
I'm certain he did not replace any tubes, they are all the same ones as when he bought it.

Hi,

I had a few Mullard GZ33's (not GZ34's) at one time and did sell a few out with some of the kits (at extra cost for the Mullard tube). Unfortunately I don't have anymore of these here in stock ... The GZ33 is taller than a GZ34 and is not an exact replacement for the GZ34 as it draws a little more current. I wouldn't use it in a STOCK ST-70 but it will work OK in your amp which has an upgraded power transformer. The height of this tube may also be an issue if you use a tube cage on your amp. I am not sure if a tube cage will fit on the amp with a GZ33 in there. Upscale Audio sells these Mullard GZ33's for $90 each + shipping. This is less money than you would pay for a new Mullard GZ34 - IF you can find one anywhere for a reasonable price. Most new NOS Mullard GZ34's are well over $100 each ...

Bob

LEVLHED

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Post n°5

Re: Choices in rectifier tubes for VTA?

by LEVLHED on Wed Nov 18, 2009 10:34 am

This would've been a completed amp that you built probably 3 or 4 months ago and sent to a customer in PR. Are you building and selling so many of these that you can't keep track of what went where? I hope that is the case!

Lets say it doesn't have the hole that indicates it's a Mullard (which it sounds like that is likely the case), are there other date codes/etc to indicate if it's one of the older USA production runs?

Bob Latino

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Post n°6

Re: Choices in rectifier tubes for VTA?

by Bob Latino on Wed Nov 18, 2009 10:54 am

Hi,

The amp that I sent to Puerto Rico went out over a year ago in February of 2008 .... The ORIGINAL buyer did not buy that wired ST-70 from me recently although the person that you bought the amp from could have purchased it recently from the original buyer within the past few months?

Sylvania hasn't made any tubes in at least 20 years. I don't know the production codes for these tubes. Maybe you can find some information on your Sylvania GZ34 if you ask the question on the Tube Audio Asylum here > Tubes Audio Asylum

Bob

LEVLHED

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Post n°7

Re: Choices in rectifier tubes for VTA?

by LEVLHED on Wed Nov 18, 2009 11:21 am

The seller made it sound like he'd bought it directly from you, maybe I was reading into how recent it was based on the number of hours he claims it was run. If I had to guess, this is the one you shipped 02/2008 and I bought it from the original owner...who apparently hardly used it!
His ad read:
For sale a used Dynaco Stereo 70 built by Bob Latino. It was built from new parts by Bob Latino and performs at its best. I estimate this unit has between 50-100 hours at the most. This one has the tube cage also which is $50 more to the listed price. I purchased this one completely assembled by Bob. Google Bob Latino ST-70 for more information.

Thank you for your help and info! I truly appreciate it.

LEVLHED

LEVLHED: Posts: 21
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Post n°8

Re: Choices in rectifier tubes for VTA?

by LEVLHED on Wed Nov 18, 2009 12:36 pm

Since I'm fortunate to not only have a job, but to also have one that is about a half mile from my house, I went home for lunch to investigate. I found what appears to be a "hole" in the center pin! I'd call it more of an indent than a hole, but judging from what I've seen so far this would indicate that it was in fact made by Mullard? Sorry the pic is a little blurry, I was being a bit hasty.

LEVLHED

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Post n°9

Re: Choices in rectifier tubes for VTA?

by LEVLHED on Wed Nov 18, 2009 1:11 pm

I suppose if it were made by Mullard, it'd be marked as made in Gt Britan, not U.S.A

Still must be a good tube though.

Jhoman

Jhoman: Posts: 25
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Post n°10

Re: Choices in rectifier tubes for VTA?

by Jhoman on Sun Jan 17, 2010 10:20 am

I found an old RCA 5U4G that appears to be in good shape. Big coke bottle glass. Has anyone used one of these in place or their 5AR4? I understand the B+ voltage is not quite as high and it will require re-biasing.

I was just wondering if it was doable.

Jeff

Bob Latino

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Post n°11

Re: Choices in rectifier tubes for VTA?

by Bob Latino on Sun Jan 17, 2010 1:01 pm

Hi Jeff,

You can use a 5U4 in place of a 5AR4. The only issue you may run into is that a 5U4 has a higher voltage drop than a GZ34 and your B+ voltage will be lower which will result in the loss of a few watts of total output. I suggest a 5U4 as a BACKUP rectifier in the ST-70, ST-120, Mark II, Mark III or Mark IV. The nice thing is that you can find quality older USA made 5U4 rectifiers at much lower prices than older USA made 5AR4's. Many older tube color TV's of the 1960's used a 5U4 for a rectifier so the supply of 5U4's as used tubes is still fairly plentiful.

As to rebiasing > Anytime you change the rectifier tube you should rebias even when changing one 5AR4 for another 5AR4 of the same brand. Each rectifier tube is slightly different from the next and will provide a slightly different B+ DC high voltage.

Bob

Jhoman

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Post n°12

Re: Choices in rectifier tubes for VTA?

by Jhoman on Sun Jan 17, 2010 1:33 pm

Well, the RCA 5U4G coke bottle never lit up, nothing so I tried a GE 5U4GA that has dots in the shape of a D below the 5U4GA. Had to bring the bias up from .34 to .55 VDC, I really don't miss any power, actually this is the best this amp has sounded since I got it. What gives with this? I did order 2 Ruby 5AR4's and will try them when they get here, but I think I'll be hard pressed to improve off the old GE 5U4GA!

Thanks Bob!

Bob Latino

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Post n°13

Re: Choices in rectifier tubes for VTA?

by Bob Latino on Sun Jan 17, 2010 2:27 pm

Jhoman wrote:Well, the RCA 5U4G coke bottle never lit up, nothing so I tried a GE 5U4GA that has dots in the shape of a D below the 5U4GA. Had to bring the bias up from .34 to .55 VDC, I really don't miss any power, actually this is the best this amp has sounded since I got it. What gives with this? I did order 2 Ruby 5AR4's and will try them when they get here, but I think I'll be hard pressed to improve off the old GE 5U4GA!

Thanks Bob!

Hi Jeff,

The fact that the 5U4 possibly sounded slightly better may have something to do with the lower voltages of the 5U4. Possibly the amp may now have a "more rounded tone" with the lower voltages involved. Your KT88's are now being operated at voltages considerably below the level that they were designed for. If you keep the 5U4 in there you should get "more mileage" (longer tube life) out of those KT88's.

Bob

RichJB603

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Post n°14

Re: Choices in rectifier tubes for VTA?

by RichJB603 on Wed Sep 08, 2010 8:12 pm

Would there be any advantage to using the GZ33's over the 5AR4 in a standard VTA-120 with upgraded caps? Other than it being slightly cheaper than std mullards?

Bob Latino

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Post n°15

Re: Choices in rectifier tubes for VTA?

by Bob Latino on Wed Sep 08, 2010 8:25 pm

Hi,

No other real advantage of using a Mullard GZ33 other than they are cheaper to find NOS than a NOS Mullard GZ34. One other thing about the Mullard GZ33. It is a lot taller than a GZ34. If you have a tube cage on your amp, I am not sure that a Mullard GZ33 will fit under the tube cage. If someone is using a GZ33 with their ST-70 or ST-120 and has a tube cage maybe they could comment here?

Bob

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