VTL ST 150.. 12BH7 suggestions

[Monad]

***the actual question starts at "SO" below. if you'd like to ignore everything before that ;D --> all good. i tend to go on, in the mornings, with the coffee flowing.

i spent some time with AI yesterday, researching 12BH7/ 12AT7 replacements for the new to me, VTL amp. good info but I did call out some hallucinations in the response so, prob good to talk to real folk, albeit, in post.

- a new to me VTL ST150 hit town, a few weeks back. had some issues with it but have been sorted $ with an additional spend.

i replaced the 2 quads of new issue Svetlana--> SINO (svetlana in name only) new issue tubes, bleh, with 8 of their more refied, better raised cousins.

partial resto- there was some work done on the unit, seems like a fairly deep roll, minus the 4 top cans. everything seems to be running well.. and with the hours, newish dead on matched 8ctet.. as soon as I get my LK150 back, this one is going for a refresh of the cans, replace the replaced coupling caps and prob everything resistorish, regardless of what was replaced already, if not up to 'quality' level.

complication- i borked my tester, going through a pile of 12AU7 and I didn't get to the tubes in the amp.. outside of replacing the 6550

right meow, it's easier to buy a few pairs of 12AT7 and 12BH7 than to find someone, in the Great Audio Gear Desert i live in, to tune up my Hickok 600a..

***SO- i started to dig into voicing for the VTL ST150 and what each tube option, 12BH7 RCA, GE, Tung Sol, Raytheon.. and wider options for what 12AT7 delivered, when working in concert.

ears- i'm looking for suggestions for both tubes, clean airy holo, unlacquered top/ mid and a well defined bass .. in that order of importance.

i have several pairs of both tubes, from a few years of hoarding but no way to test or know if they're any better than what's in there so.. figured, start 'selectively collecting' a few matched options, just to make sure I'm at bingo, when i flip that switch.

Any suggestions here, greatly appreciated.

right now, the sound is really nice--> tube preamp, clean digital section, into some fully restored ESS AMT1 Towers.

- I ran it in triode, 60w first, then after a few days- 30+ hours of chill, low key play, switched it to tetrode, which delivered, imo, more of what I was looking for, from these funky +speakers.

 

[knotscott]

It's subjective and tubes will sound a bit different in different circuits, but in my Dyna/VTA amps the US made Tung Sol 12BH7a has been wonderful as a voltage driver.

 

[gadget73]

A 12BH7 is very much not a sub for a 12AT7. Its in the ballpark for a 12AU7 though, which is where it commonly gets used. Similar gain, bias, etc. A 12AT7 is like 3x the gain of a 12BH7.

 

[Lavane]

It's subjective and tubes will sound a bit different in different circuits, but in my Dyna/VTA amps the US made Tung Sol 12BH7a has been wonderful as a voltage driver.

I agree. I have one in my VTA ST-70 and M-125 mono blocks.
I didn't really hear a difference between a 12AU7 and 12BH7 for the long tail pair though.
The OP's amp uses two 12BH7's and two 12AT7's. I downloaded the manual it doesn't have a schematic, or state what driver tubes do what.

 

[Monad]

from

A 12BH7 is very much not a sub for a 12AT7. Its in the ballpark for a 12AU7 though, which is where it commonly gets used. Similar gain, bias, etc. A 12AT7 is like 3x the gain of a 12BH7.

from what i understand and am looking at, each side has 4 6550 and a 12BH7/ 12AT7.. so i was more asking what's good for each value, then also, how do they interact to hump the sound.

my typical path is, buy this, buy that, change this.. limited method or modality beyond what's available for cheap enough, at the time but I could try to plan ahead or at least have some idea of how they work together.

 

[Monad]

I agree. I have one in my VTA ST-70 and M-125 mono blocks.
I didn't really hear a difference between a 12AU7 and 12BH7 for the long tail pair though.
The OP's amp uses two 12BH7's and two 12AT7's. I downloaded the manual it doesn't have a schematic, or state what driver tubes do what.

it sucks that there's no published spec. its not like I'm going to ship a 90lb amp to VTL and back and from what I understand, they're not trying to work on the older VTL gear...

..on the way good chance it becomes a brick, on the way back, same thing but likely after spending several pockets of monies-unknown.

 

[gadget73]

and a 12BH7/ 12AT7

do you mean its one of each, or either/or ? I interpreted it to mean either/or, and what I was saying is that a 12BH7 is not generally considered to be a sub for a 12AT7. If thats what you meant, I'd question whether the mfg actually says that either can be used in that spot or if you got some bad info from someplace.

If you mean one of each, then disregard.

 

[spantou01]

I assume OP is asking for suggestions for new tubes to “roll” at both the 12AT7 as first amplifier stage and 12BH7 as driver stage respectively. Since most of the important amplification will be done in the first 12AT7 stage OP will be more likely to hear a difference by “rolling” that tube, rather than the 12BH7. So, although I know nothing about the details of this VTL amp, my suggestion would be to buy new 12AT7s and try them first. Then, if you are still missing the secret sauce, try good 12BH7s by all means.

Personally, the best NOS 12AT7’s I have heard were the Mullard M8162 tubes, but I have not listened to a great many 12AT7 on good amplifiers.

12AT7 Tubes in Stock

Brent Jessee’s listing of the various 12AT7 types would be informative if OP is not aware of it.

 

[Mr Boochie]

Personally, the best NOS 12AT7’s I have heard were the Mullard M8162 tubes, but I have not listened to a great many 12AT7 on good amplifiers. Brent Jessee’s listing of the various 12AT7 types would be informative if OP is not aware of it.

The 6201/12AT7WA is a nice tube, too. I like mil-spec GE and Sylvania ones.

 

[Lavane]

I assume OP is asking for suggestions for new tubes to “roll” at both the 12AT7 as first amplifier stage and 12BH7 as driver stage respectively. Since most of the important amplification will be done in the first 12AT7 stage OP will be more likely to hear a difference by “rolling” that tube, rather than the 12BH7. So, although I know nothing about the details of this VTL amp, my suggestion would be to buy new 12AT7s and try them first. Then, if you are still missing the secret sauce, try good 12BH7s by all means.

Personally, the best NOS 12AT7’s I have heard were the Mullard M8162 tubes, but I have not listened to a great many 12AT7 on good amplifiers.

12AT7 Tubes in Stock

Brent Jessee’s listing of the various 12AT7 types would be informative if OP is not aware of it.

If the 12AT7's are the voltage gain tubes, then, ya I would be trying different 12AT7's instead of the 12BH7's. I tried a EH 12BH7 in my ST-70. Its a short plate 12BH7? It was shorter than my Phillips, Siemens, and Sylvania 12BH7's.
I didn't like it and put an old stock 12BH7 back into the amp.
If the 12AT7's are the first gain stage tube it's going to effect the overall sound more than the 12BH7's I would think.

 

[Mr Boochie]

If the 12AT7's are the voltage gain tubes, then, ya I would be trying different 12AT7's instead of the 12BH7's. I tried a EH 12BH7 in my ST-70. Its a short plate 12BH7? It was shorter than my Phillips, Siemens, and Sylvania 12BH7's.
I didn't like it and put an old stock 12BH7 back into the amp.
If the 12AT7's are the first gain stage tube it's going to effect the overall sound more than the 12BH7's I would think.

As far as I know, the 12BH7 is a good tube for current swing. Better than the 12AU7, with the same mu-factor. The 12BH7 needs more heater current, so it’s not exactly a 1:1 replacement for the 12AU7. I am not sure that the Russian 12BH7 has the same specs as the early US-made ones.

The 12AT7 has a higher current swing than a 12AX7. So maybe that’s why it was used in the unit’s first gain stage.

 

[mcgjohn]

I used to have that amp a number of years ago. Which version do you have?

Before you get too far down the road would suggest you add some 0.1uf film caps across the main filter caps. These will help filter out switching noise from the bridge.
if you like bass you may want to try GL or EH KT88s in place of the 6550s.

If your tester out to lunch just order some new 12BH7s.

you may want to get the large capacitors at least tested. They are known to dry out from the tube heat exposure.
Also the snap mount caps on the under side of the PCB should be tested or replaced. They get worked pretty hard.

 

[Hi-FiGuy]

If you want a beefy 12AT7, try the 7062. This tube is a bit taller and uses more fil current, but is a very nice tube.

 

[Mr Boochie]

If you want a beefy 12AT7, try the 7062. This tube is a bit taller and uses more fil current, but is a very nice tube.

Amperex PQs

 

[Monad]

I used to have that amp a number of years ago. Which version do you have?

Before you get too far down the road would suggest you add some 0.1uf film caps across the main filter caps. These will help filter out switching noise from the bridge.
if you like bass you may want to try GL or EH KT88s in place of the 6550s.

If your tester out to lunch just order some new 12BH7s.

you may want to get the large capacitors at least tested. They are known to dry out from the tube heat exposure.
Also the snap mount caps on the under side of the PCB should be tested or replaced. They get worked pretty hard.

i bought the amp, after a partial restoration was done on it.. besides coupling caps, and 4 cans on top, power line and other bits were done by a tech in Minneapolis, prior to the sale.

i have an LK150 at a tech right now.. once that's back, I'll be sending this out for a head check/ refresh for everything not boo-gee enough.

the VTL ST150 is an amazing amp, it really is. 60w triode joy, 150 tetrode. super versatile. w the LK I'll be covered on tube amps, for most speaker occasions.

.. have some Quicksilver 8417 that were modded to a VTL ST50 circuit a few years back.. but I left them in triode 17w. taking it back in to have the switch reconnected, just to cover that 35ish watts space.

getting back to that happy point, where most of my gear is fixed or for sale, funding future fine tuning.

!!!good info on the 12AT7 being the driver for SQ. i have a few in the cart right now, figure I can just sample and see, if and then which one.

i'l prolly pick up matched 12BF7, just to make sure what's coming in, is similar on both sides, to what's going out.

 

[Monad]

I used to have that amp a number of years ago. Which version do you have?

Before you get too far down the road would suggest you add some 0.1uf film caps across the main filter caps. These will help filter out switching noise from the bridge.
if you like bass you may want to try GL or EH KT88s in place of the 6550s.

If your tester out to lunch just order some new 12BH7s.

you may want to get the large capacitors at least tested. They are known to dry out from the tube heat exposure.
Also the snap mount caps on the under side of the PCB should be tested or replaced. They get worked pretty hard.

I meant to post some pics.. almost seems obligatory but got sidetracked.

have the early model faceplate. wanted the fancy new-er one but for over a Gmore, probably not worth the pretty bump.

on a high note, with the USB fans pointed up, sitting over the transformers, I also have a solid room heater for winter.

 

[mcgjohn]

I meant to post some pics.. almost seems obligatory but got sidetracked.

have the early model faceplate. wanted the fancy new-er one but for over a Gmore, probably not worth the pretty bump.

on a high note, with the USB fans pointed up, sitting over the transformers, I also have a solid room heater for winter.
View attachment 3865205

cool.

yes that is the series 1.

I don't think I saved any photos I can pass along. The larger power output units (newer versions with the glass in the faceplate) did have a substantial increase in weight as the transformers got substantially larger.

You may want to at least test the ESR and capacitance on the power supply caps to make sure the heat has not cooked them.
I normally run these amps with the tube cage removed to let the heat out. The amp will run cooler. That is assuming you have no young kids around that
may stick their fingers into a hot tube amp.

 

[mcgjohn]

i bought the amp, after a partial restoration was done on it.. besides coupling caps, and 4 cans on top, power line and other bits were done by a tech in Minneapolis, prior to the sale.

i have an LK150 at a tech right now.. once that's back, I'll be sending this out for a head check/ refresh for everything not boo-gee enough.

the VTL ST150 is an amazing amp, it really is. 60w triode joy, 150 tetrode. super versatile. w the LK I'll be covered on tube amps, for most speaker occasions.

.. have some Quicksilver 8417 that were modded to a VTL ST50 circuit a few years back.. but I left them in triode 17w. taking it back in to have the switch reconnected, just to cover that 35ish watts space.

getting back to that happy point, where most of my gear is fixed or for sale, funding future fine tuning.

!!!good info on the 12AT7 being the driver for SQ. i have a few in the cart right now, figure I can just sample and see, if and then which one.

i'l prolly pick up matched 12BF7, just to make sure what's coming in, is similar on both sides, to what's going out.

you can experiment with that first input tube. It has a pretty significant effect on the sonic signature of the amp.

 

[Monad]

cool.

yes that is the series 1.

I don't think I saved any photos I can pass along. The larger power output units (newer versions with the glass in the faceplate) did have a substantial increase in weight as the transformers got substantially larger.

You may want to at least test the ESR and capacitance on the power supply caps to make sure the heat has not cooked them.
I normally run these amps with the tube cage removed to let the heat out. The amp will run cooler. That is assuming you have no young kids around that
may stick their fingers into a hot tube amp.

so the original FS ad had a pic of the restoration parts.. tried to post here but getting 'file to large' errors on every pic uploaded, jpeg or larger.

Based on the image, Grok identified the following as likely restoration points, from the bits in pic.

• Large black can electrolytics (the two front cans that were swapped) — Japanese-style high-voltage cans. No clear brand stamp visible; these are commonly replaced with Nichicon, United Chemi-Con, or Rubycon equivalents in these restorations.
• Green cylindrical capacitors (multiple smaller units) — Look like film or hybrid film/electrolytic types used for coupling/bypass. Brand markings not legible; frequent choices in this position are Mundorf, Wima, or Elna-style film.
• Smaller black cylindrical units — Additional electrolytics or film caps. Brand not readable.
• Cluster of discrete parts (resistors and small passives) — Mixed resistors and components. No color bands or brand text clear enough to identify (common replacements include metal-film types from Vishay, Panasonic, or generic).

The 1600uF high voltage capacitors will be replaced at next go around, along w higher end coupling caps.. but I'm not going to flip again for a pic, until I nail down a tech to do the work.

What else should I look into replacing?

Without a spec, it's just going to be a parts swap then test install.

 

[Monad]