Tube Availability

[mhardy6647]

A storied name in early high-end. Mark was responsible for one of the most highly acclaimed preamps of the '70s, the Paragon. At least in the underground circuit. Generally rated better than the then ne plus ultra ARC SP-3 variants, and often compared with the JC-2..

FWIW (which, admittedly, ain't much) he also seems to be, based on my interactions with him, a genuinely nice guy -- which counts for a lot in my book, as well.

 

[anmpr1]

The 6922/6DJ8/E88CC tube at least used to be very highly regarded. The Audible Illusions Modulus 3A preamp is damned popular and was designed around that tube. A lot of preamps use/used it.

Michael Elliot of the erstwhile Counterpoint company used 6DJ8 in his designs. I was using his SA-3 preamp at the time, along with his SA-2 MC stage (also using multiple 6DJ8s). But I couldn't get the SA-2 noise down, for use with the Denon or Highphonic MC cartridges. I found the little Marcof battery powered unit to be much quieter--the Marcof was a take-off (Marshall Leach called it a rip off) of his Audio magazine DIY project.

Later, after Counterpoint took a knee, Elliot wrote on his blog that use of the 6922 (or any tube) in a MC stage was wrongheaded, due to noise problems. Instead, he advised the use of a good transformer.

An interesting cosmetic approach, Counterpoint mounted the 6922s horizontally, so the unit fit the 1U form factor. It looked like the early Mark Levinson preamps, no doubt on purpose.

 

[JeffS7444]

Looks like Western Electric-branded 5755 (not 5751) are currently selling for around $100/ea on That Auction Site. The last time I bought, I think it was for $1.50 apiece, and if I had an inkling of this craziness, I'd have bought more than a half-dozen.

 

[SIY]

I can’t remember the company that Roger Modjeski did a preamp for back in the 70s, but also an all 6DJ8 design.

Sad reality is that there’s no tube quiet enough for LOMC input stages. The only way to make that work is a transformer, and correct implementations can be counted on the fingers of one mangled hand.

One other comment: the SP3 was basically a copy of the Marantz, and was frankly a poor preamp.

 

[anmpr1]

Looks like Western Electric-branded 5755 (not 5751) are currently selling for around $100/ea on That Auction Site. The last time I bought, I think it was for $1.50 apiece, and if I had an inkling of this craziness, I'd have bought more than a half-dozen.

Yeah. Who would have thought to dump their retirement portfolio into NOS tubes, and four paks of metal and high bias Maxell cassettes? But if we had, we'd be doing better than Bitcoin!

 

[JeffS7444]

An interesting cosmetic approach, Counterpoint mounted the 6922s horizontally, so the unit fit the 1U form factor. It looked like the early Mark Levinson preamps, no doubt on purpose.

Those were pretty, but man did they have RFI problems. Not well-shielded, and I don't recall if they incorporated grid stoppers, either.

 

[anmpr1]

I can’t remember the company that Roger Modjeski did a preamp for back in the 70s, but also an all 6DJ8 design.

One other comment: the SP3 was basically a copy of the Marantz, and was frankly a poor preamp.

Roger did the electronics for Harold Beveridge. That sticks out in my mind.

The problem with the SP-3 is you could never keep up with it. How many mods were there? As soon as you had the latest, Bill Johnson had another one in the pipeline. Must have been a nightmare to be an ARC dealer, trying to keep up with it. LOL

 

[Godataloss]

I can’t remember the company that Roger Modjeski did a preamp for back in the 70s, but also an all 6DJ8 design.

Sad reality is that there’s no tube quiet enough for LOMC input stages. The only way to make that work is a transformer, and correct implementations can be counted on the fingers of one mangled hand.

One other comment: the SP3 was basically a copy of the Marantz, and was frankly a poor preamp.

I just picked up a Fosgate Signature yesterday. It's quiet as a church mouse on my very efficient speakers so far. 7 tubes, including 2, 6 dj8s. I only listened to one album side last night, but it seems definitely an improvement over my Parks Audio Budgie (also 2 6 dj8s and quiet as a church mouse). The fosgate has a tranny, but it's just used to feed some big caps that load the tubes. Please forgive my novice explanation.

Edit- I should probably say I haven't run it in high gain as I'm currently using a Ortofon Black cart.

 

[JeffS7444]

What about simply making tubes last longer? From my days working at television stations, I recall the procedure of bringing the tube filaments up to temperature before bringing B+ online, wonder if that procedure could benefit audio amplifiers too.

 

[SIY]

What about simply making tubes last longer? From my days working at television stations, I recall the procedure of bringing the tube filaments up to temperature before bringing B+ online, wonder if that procedure could benefit audio amplifiers too.

There’s a nice discussion of this in “Valve Amplifiers.” Generally no, but there’s some very specific exceptions.

 

[MattHooper]

Most of them are probably not noise-critical. And if you're intrepid, you can replace the ones used as a CCS by a better, non-tube CCS, leaving the tubes to do amplification rather than housekeeping.

Hey SIY, question for you:

Over the years I've simply replaced all my output tubes if I notice the sound is getting gritty or distorted. (I've had them last up to 6 years of pretty constant use). But I've been stocking up so...

I have a variety of tubes for my CJ Premier 12 monoblock amps. For instance I have NOS Svetlana Winged C 6550s and the newer Tung Sol 6550s. If I have all Svetlana tubes in the amps and one tube goes bad, I presume that just replacing it with one of the newer Tung Sol 6550s would be fine, is that correct? (My amp allows user biasing for each tube).

In fact, while I'm asking...I also have KT120 tubes that work well in the amp. If I had all KT120s in the amp and one went bad, would it be ok to substitute a 6550 tube? My layman's hunch is that sounds a bit more dicey.

Thanks.

 

[SIY]

Hey SIY, question for you:

Over the years I've simply replaced all my output tubes if I notice the sound is getting gritty or distorted. (I've had them last up to 6 years of pretty constant use). But I've been stocking up so...

I have a variety of tubes for my CJ Premier 12 monoblock amps. For instance I have NOS Svetlana Winged C 6550s and the newer Tung Sol 6550s. If I have all Svetlana tubes in the amps and one tube goes bad, I presume that just replacing it with one of the newer Tung Sol 6550s would be fine, is that correct? (My amp allows user biasing for each tube).

In fact, while I'm asking...I also have KT120 tubes that work well in the amp. If I had all KT120s in the amp and one went bad, would it be ok to substitute a 6550 tube? My layman's hunch is that sounds a bit more dicey.

Thanks.

It will likely increase distortion, since the control of characteristics from supplier to supplier is not great. Bias control will help to prevent transformer distortion, but tube mismatch is not easily fixable. Now, will it be audible distortion? That’s a much harder question, and there’s only one way to find out…

FWIW, I match my output tubes for both idle current and transconductance, but I buy a bunch of tubes at a time and cull relentlessly.

 

[Godataloss]

What about simply making tubes last longer? From my days working at television stations, I recall the procedure of bringing the tube filaments up to temperature before bringing B+ online, wonder if that procedure could benefit audio amplifiers too.

I have a couple amps with thermistors. They help preserve tube life.

 

[MattHooper]

It will likely increase distortion, since the control of characteristics from supplier to supplier is not great. Bias control will help to prevent transformer distortion, but tube mismatch is not easily fixable. Now, will it be audible distortion? That’s a much harder question, and there’s only one way to find out…

FWIW, I match my output tubes for both idle current and transconductance, but I buy a bunch of tubes at a time and cull relentlessly.

Thanks that's very helpful to know!

The question was mostly out of curiosity and also "in case of emergency" (given tube supply may be an issue in the near future). In practice I doubt I'll have to find out. For each tube type I've bought matched quads for each amp, plus a couple spares of the same tube type.

Sorry, one more question that arises from your reply. In terms of culling better from worse tubes: Are you culling more for distortion characteristics or reliability and better likelihood of longer tube life?

If I understand correctly, a lower quality tube can mean one that isn't audibly distorting more than the rest in a batch, but will for (a technical reason) likely have a shorter life span.

 

[SIY]

Thanks that's very helpful to know!

The question was mostly out of curiosity and also "in case of emergency" (given tube supply may be an issue in the near future). In practice I doubt I'll have to find out. For each tube type I've bought matched quads for each amp, plus a couple spares of the same tube type.

Sorry, one more question that arises from your reply. In terms of culling better from worse tubes: Are you culling more for distortion characteristics or reliability and better likelihood of longer tube life?

If I understand correctly, a lower quality tube can mean one that isn't audibly distorting more than the rest in a batch, but will for (a technical reason) likely have a shorter life span.

Mostly, I’m culling the ones I can’t find a good match for or that are too far from nominal for that type. For phono tubes, I look at noise and especially corner frequency.

 

[MattHooper]

Mostly, I’m culling the ones I can’t find a good match for or that are too far from nominal for that type. For phono tubes, I look at noise and especially corner frequency.

Got it. Thanks.

 

[atmasphere]

I can’t remember the company that Roger Modjeski did a preamp for back in the 70s, but also an all 6DJ8 design.

Sad reality is that there’s no tube quiet enough for LOMC input stages. The only way to make that work is a transformer, and correct implementations can be counted on the fingers of one mangled hand.

You can parallel tube sections to obtain lower noise. If you are careful to vet tubes for low noise as well, you can get acceptable performance with cartridge outputs down to about 0.2mV (meaning: its quieter than a good quality LP surface). IME I found the only way to really do that though was to use differential amplifiers employing a properly designed solid state CCS. If the CCS isn't doing its job, this won't work.

FWIW I stay away from all frame grid triodes. Good for instrumentation, lousy for audio for the reasons you stated earlier.

 

[SIY]

You can parallel tube sections to obtain lower noise.

Unfortunately, because the noise is uncorrelated, you only get 3dB per tube advantage. I tried the massive paralleling and still couldn't get it as quiet as using a 10:1 stepup transformer; because of the necessary physical size, it takes significant layout and shielding effort to not act as a noise antenna. The SUT, of course, was smaller, cooler, and lower distortion, and additionally gave me great benefit for common-mode noise rejection.

 

[atmasphere]

Unfortunately, because the noise is uncorrelated, you only get 3dB per tube advantage. I tried the massive paralleling and still couldn't get it as quiet as using a 10:1 stepup transformer; because of the necessary physical size, it takes significant layout and shielding effort to not act as a noise antenna. The SUT, of course, was smaller, cooler, and lower distortion, and additionally gave me great benefit for common-mode noise rejection.

So were you driving the SUT balanced from the tone arm then?

 

[SIY]

So were you driving the SUT balanced from the tone arm then?

Exactly. I’m a long time advocate of balanced phono connection. Both my published phono preamp designs (MM and MC) use balanced input and have reasonably high CMR. The SUT I used has excellent primary balance.