Fosgate Tube Sequence Rolling Guidelines

[all2ears]

Well it's been a few months and all Ivan's silver eclipse cables have burned in and my bank account has recovered - My next tweak attempt is to roll some tubes in my Fosgate Phono preamp to see what more I can get out of my McIntosh MT-10 turntable

I've been swapping out the stock 12ax7 for the stock 12at7 and am now familiar with the impact of these tubes - I figured before I threw any $$$ at the system I'd check direct with manufacturer to see if they had any recommendations - Mike Fajen of Musical Surroundings was kind enough to share a letter from Bob Fosgate on his view of tube impact on the preamp ....... he is the fella who designed it so Bob should know

Now I am on a quest for the elusive Telefunken 12AX7 so any help on a reliable source would be appreciated - I'm looking for some more punch to the drums !!!!

Anyway here is Bob "Foz" Fosgate's overview of his preamp and the impact of tubes

Hi Mike:

I guess tube rolling is here to stay. We did quite a bit of listening before settling in on the stock tubes. Not sure anyone knows why tubes sound different (except for gain) but they do. It comes down to listener preference, and the sound of the various components used in the playback system.
Tubes V1, V3, V4 provide most of the gain in the circuit. Tube V2 is the plate load for V1, tube V4 is the plate load for V3, tube V6 is the plate load for V5, these are used in the SSRP configuration. Tube gain in positions V3,V4,V5,V6 will have an effect on the bass. The more gain the more low bass.

The first tubes V1 and V2 (6922) are selected for low noise and channel balance and I do not recommend rolling these because more background noise and channel imbalance will likely be the result.

V3 makes a lot of difference, we chose one that sounds very good all around but replacing that tube with 12AT7 results in more detail, less smoothness, and slightly less bass. I like an old Telefunken 12AX7 in that position, it has more detail then the stock 12AT7. Fred prefers the old Mullard there which is close to the stock tube we use.

Different tubes in position V4 do not make much of a noticeable change.

Changing tube V5 to a recent production Russian or Chinese 12AT7 tube will likely reduce the detail a bit and sound a little smoother and rounder, and reduce low bass output.

Tube V6 will not make much of a change.

I hope I have not confused you more.

Foz

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I've been running this tube config and really like it

V1 & V2 Telefunken CCA 6922
V3 & V4 Amperex Holland 12ax7
V5 & V6 RCA triple mica black plate 12at7
V7 GE 6202 black plate "five star" 6x4 rectifier

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To me the Amperex are better suited for the V3 & V4 positions....the teles were a bit to relaxed when I used them in the V3 & V4 positions....always a YMMV!

[all2ears]

Jeff - I tried both a Tele and an RCA black 12ax7 in the 3 position and the sound was a bit flat so I went to the Tele 12at7 and that added some depth and warmth but I can see what you mean about relaxed (especially in the drums)

I'm going to try out a Raytheon 12DT7 this week end in slot #3

I have Amperex Bugleboy's in 5 & 6 - Most likely a bit of overkill but at least that is two slots that will be roll free for a bit

Tubes ........... the next frontier

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Originally Posted by all2ears

Jeff - I tried both a Tele and an RCA black 12ax7 in the 3 position and the sound was a bit flat so I went to the Tele 12at7 and that added some depth and warmth but I can see what you mean about relaxed (especially in the drums)

I'm going to try out a Raytheon 12DT7 this week end in slot #3

I have Amperex Bugleboy's in 5 & 6 - Most likely a bit of overkill but at least that is two slots that will be roll free for a bit

Tubes ........... the next frontier

I would try the RCA black plate back in V3 position but ditch the BB in V5 and V6 and try some RCA black plates triple mica, Amperex or Tung-Sol there. IMO the BB strengths are not dynamics, there more a rounded tone sound to me and V5 and V6 needs something with more of a kick there.....

[all2ears]

Jeff - I thought Amperex made the Bugleboy 12AT7 ... am I missing something?

For the V3 & V4 slots I've been switching between Telefunken 12AX7 and Raytheon 12DT7 - I should have a few of the RCA black plates to try out next week - You make good recommendations so the RCA tubes are much anticipated

Tube rolling ............. how I'll spend 2012

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The BB are really nothing speacial in the 12at7 family....the late 50s 12ax7 are a different story....anyway its a long read but may help you.

Here some info I dug up that may help you with different types:

12AT7:
The "garden variety" of USA made versions of this tube. All I have seen have the wing shaped plates. The early versions have blackplates, the later (1960s, 1970s) have greyplates. All seem to be top getters, with either a square or D shaped top getter. All are great tubes, and the finest (like the RCA blackplates) are on par with the military and industrial versions. Sometimes "selected" versions of this tube turn up. Often made by large manufacturers like RCA, they are usually labelled with the brand of the product they were selected for. Most often electronic organ brands are found on the label like Baldwin, Wurlitzer, and others. Sometimes hi-fi and musicial instrument amps had select tubes made for them, and labels like McIntosh and Fender turn up. The tips of these tubes are usually painted a color, indicating they have been screened for low noise. These tubes are a great buy when they turn up!

12AT7WA:
This is a military version of this tube, and may also be listed as a 6201. Some tubes have both type numbers on the label. These usually have thick mica spacers. The RCA versions have extra support posts and tiny "12AX7" type plates, nearly always black. This tube is usually very low in microphonics due to it's rugged construction.

6201:
Frequently, this number appeared along with 12AT7WA (military version) on the same tube. However, some brands made the 6201 as an "industrial" 12AT7. Sylvania made a 6201 in their Gold Brand line, and it came in the distinctive gold box, had gold lettering on the glass, and most (but not all!) had gold plated pins. Amperex made a very nice PQ version of the 6201 with gold pins. A few 6201 tubes, usually early ones, have an extra mica spacer on top, known as "triple mica", and are noted for lower microphonics. Overall, this tube is a step up from the standard 12AT7, and most were made to meet military specs so that both military and industrial versions could be manufactured on the same assembly line.

6211:
This unusual tube is listed as a frequency halfer, in addition to being a class A amplifier dual triode with medium mu. Medium mu means it has lower gain than the typical 12AT7, in fact lower than even the 5965 listed below. It also has much larger, flat plates that have diamond shaped points at the corners bent inwards (in the versions I have seen) that seem to add rigidity to the plate structure. This tube also has slightly lower plate voltage and current ratings, but not enough to make a difference in hi-fi use. I have seen it used in preamp circuits, and it's lower gain and lower microphonics (thanks to the large plates) probably contribute to a mellow sound. I have an amp where this tube is used interchangeably with a 12AT7, and there is a difference in sound between the two types. These are hard to find, but you may want to try them to see how a medium-mu tube sounds in place of the standard 12AT7. Just the thing to tame down a screaming guitar amp or shrill stereo system.

5965:
This industrial tube is close enough to the 12AT7 that audiophiles have started buying them up and commenting on the low noise of this tube. It most likely is because it has a lower gain, a mu of 47 compared to 60 of a 12AT7. It is kind of like using a 5751 in place of a 12AX7--the lower gain being the main difference. These tubes are still plentiful, and are really well made. GE made a fine version of this tube in their "5-Star" broadcast line. A few have an extra mica spacer on top, known as "triple mica" and noted for lower microphonics. There is also a rare Telefunken version of this tube with long plates.

E180CC or 7062:
Most often found in European types, typically Amperex or Philips, this tube is virtually the same as a 5965 in regard to electrical specifications. Audiophiles have been seeking it out since the price is generally lower than the premium ECC81 NOS prices currently. Like the 5965, it has slightly lower gain than the 12AT7, and has the added advantage of a 10,000 hour heater life to make it another audiophile "secret" tube. A super bargain when you find them, since they are musical and smooth to listen to, and actually sound better than many standard 12AT7 tubes. Better grab them now while the prices are still low! This tube is about a half-inch taller than the standard 12AT7, so chassis space is an important consideration.

6414:
An industrial, computer rated dual triode,virtually the same specs as the E180CC or 7062 listed above. Unlike the E180CC, this tube was made in the USA. It is a more rugged build, with the Raytheon blackplate type sporting triple mica and military ratings. This tube is also like a 12AV7 and will work wonders in any 12AT7 spot, and may be just the ticket if you want to boost the gain of a 12AU7 circuit. The 6414 is getting very hard to find, but with a 10,000 hour heater rating you may never need a replacement. Discussion groups rate this type very highly for use in headphone amps. Stands about 1/2 inch taller than the standard 12AT7.

6829:
Yet another industrial tube that is very similar to the 5965. This one has a mu factor of 47 so it is slightly lower than the typical 12AT7. Those I have heard are rich, detailed, warm, and thanks to the lower mu, very quiet and low in microphonics. GE made these in their 5-star and military line so they are a rugged and long lasting tube. Like the E180CC, this tube is about a half-inch taller than the 12AT7, so you need to consider overhead chassis or cabinet space when swapping a 12AT7 with one of these. An excellent audio bargain now, but prices may soon climb as audiophiles discover them!

6679:
This is an industrial 12AT7 designed for mobile communications use. It maintains it's output even if the filament voltage varies. Nice tubes, but they never have been too plentiful. They will work fine in hi-fi use, and are a step up in quality from the standard 12AT7.

7728:
This was a high-end industrial tube made by CBS or Hytron (same factory made both, actually) with gold pins. These are nice tubes, but are very scarce. I rarely have them in stock.

ECC81:
This is the European version of the 12AT7, and is identical to it. The Telefunken even has the wing shaped blackplates, just like the RCA. Great tubes, equalled only by the RCA blackplate or the military/industrial versions. Even those made for USA hi-fi products in the 1960s (Knight, Bogen, Daystrom, Dynascan, etc.) are excellent tubes, and have the fine sound quality of those with Mullard, Amperex or Telefunken labels. These tubes currently are a bargain, and they blow away the Russian and Chinese trash being made today. The rarest are the 1950s versions of Mullard and Amperex with a "D" shaped top getter said to sound on par with the scarce A2900 listed below.

E81CC or ECC801S:
This is a rare tube, usually found only in the Telefunken or Siemens brand. These tubes have been screened for audio use and low noise, and have a 10,000 hr. rated life on the heater. The ECC801S are by far the rarest, and the E81CC only a little more common. Both are excellent, low noise, finely crafted tubes, with the E81CC being the best value currently when compared to the recent spiraling rise in the ECC801S prices. They are both rare, but if you find some they may well be the last 12AT7 tube you will ever need to buy!

TS65:
This stands for "Telefonica Serie", and these rare gold pinned gems were made for various European telephone networks. As most European countries had government controlled telephone and communications networks, these tubes were made for the government and are essentially military spec. This would include features such as 10,000 hour heater life, gold pins, matched internal triode elements, low noise, uniform output under harsh operating conditions, in short, the whole enchilada. Most were labeled for Philips, rare ones were made by Valvo. Watch for the uber rare 1950s D getter and pinch waist versions. I would stack them up against the very best NOS ECC801S and A2900 tubes in quality!

CV4024 and M8162:
Fine British military tubes from the 1960s and early 1970s. I have seen mostly Mullard examples of these, although Brimar did make some. Depending on the manufacturer, the tube may have both numbers on it. The rarest and best are the early Mullards labeled with M8162 and the shield logo. These are all military tough, and have that sweet rich British tube sound. Most of the Mullard military tubes were made at the Mitcham, UK factory, which made most of the British military tubes.

CV455:
Another British military type of 12AT7. Usually Brimar was the maker of this fine tube, with the earlier versions from the 1950s being the most desirable. Watch for the versions made in the 1970s. These have wing shape black plates and a sound close to the earlier type, at often half the price!

6060:
This rare tube is the Brimar answer to the Genalex A2900. It has a similar construction to it. These are sometimes called the "Yellow-T" tube due to the large capital letter "T" in a yellow triangle on the glass. The best of these were made by Brimar at their Footscray, UK factory in the 1950s. Virtually all of these are phono grade, they are very quiet. There are later versions with the "T" logo on a white triangle, but these are not as desirable, sonically, and when found should not be nearly as expensive. The Yellow-T tubes are remarkable for their air, realism, and seductive warmth, and unfortunately are getting as rare as the A2900 tubes!

A2900:
The even scarcer A2900 is in the "Gold Monarch" series by Genalex. Genalex was the premium line of tubes produced by the Marconi-Osram Company in England. It has wide, flat black plates and white lettering on the glass, the words "Gold Monarch" in white script, with the red Genalex decal logo around the top of the tube. There is also a British domestic version with the grey and blue GEC decal on the glass, that was not exported. These are true audiophile tubes, with tightly controlled noise specs, designed with audio perfection in mind. Any scarcer and these would be museum pieces!
OK, SO TELL ME HOW THEY SOUND!!

TELEFUNKEN, SIEMENS, VALVO, LORENZ, and other German made NOS: These tubes are usually characterized by an impressive open "air" at the top end. The soundstage is large, even in mono applications these tubes have a great 3-D image. The midrange is ruler flat, and the bass is tight and accurate. These tubes have a fine sense of dynamics, and most are impressively quiet. These are not "warm" tubes, and to some ears their lack of midrange warmth may be heard as bright. I tend to think of them as accurate, and their clean, focused sonic image is astonishing. My personal favorites. For critical phono or microphone preamp needs, grab the rare Telefunken or Siemens ECC801S before they are gone! They are absolutely incredible tubes that will never be made again!

AMPEREX, PHILIPS, MAZDA and other Holland/France/Belgium made NOS: These tubes are a great balance of a clean, airy top end, nice midrange warmth, and accurate bass. They are very pleasant, clean, and musical to listen to in hi-fi applications. Unlike other clean European tubes, these break-up impressively when overdriven in a guitar amp. The rare longplate versions are the same, but with even more soundstage space and detail. The Mazda adds a nice bit of dynamic punch to the sound.

MULLARD, GENALEX, BRIMAR, and other British made NOS: Like a warm British jacket of the finest tweed, these glorious tubes have an attractive sweet warmth in their midrange and lower regions. The top end is silky and pleasant, without being rolled-off. The best of these tubes retain a fine sense of "air" at the top, and the upper midrange is smooth and liquid. These tubes reproduce the human voice, especially female voices, with haunting realism. The rare D-Getters and Genalex versions have an eye-popping huge soundstage, razor sharp focus and detail, and an uncolored top end while retaining the warmth of the lower priced versions.

RCA, RAYTHEON, GE, SYLVANIA, and other USA made NOS: This group is very diverse. The RCA, Raytheon, and Sylvania blackplates are among the best here. These are very musical tubes with air and sparkle at the top end, warmth in the mids, and great bass. The RCA are drop dead beautiful in guitar amps, even the lower priced greyplate and longplate versions. They also have a wonderful "phat" gritty sound when overdriven in these amps. The blackplates and most tubes made for organs are very quiet. The greyplate GE is an all-around nice-guy tube to listen to, the blackplate here possibly getting the nod for hi-fi use. The Sylvania greyplate and military versions are clean and a bit bright, but the Sylvania 6201 variants are very balanced and pleasant to listen to for hours. The RCA 6201 and 5965 is more like the Mullard, with a rich warmth and wide bandwidth. Currently, the USA made tubes are a nice surprise with their low prices as compared to the European types

[Myles B. Astor]

The 801S is King of the Hill and everything else is second!

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Originally Posted by Myles B. Astor

The 801S is King of the Hill and everything else is second!

....

[all2ears]

WOW ..........Thanks Jeff - This will require some reading and reading and reading

Terrific information