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In Reply to: RE: Anyone try 6BL8 as a driver in ST70? posted by bcguitar on April 26, 2010 at 14:09:34
bcguitar,
As others have mentioned, the 6BL8 has a different pinout than the 7199. I think there is more than one replacement board for the ST70 that uses the 6GH8A.
The 6BL8 is part of a family of tubes that as far as I can tell are more or less interchangable:
6GH8, 6U8, 6BL8, 6EA8 ratings:
tube....pentode Trans.....power.....triode Trans....power
6GH8....8500 umhos......2.5W......7500 umhos....2.5W
6U8.......7500 umhos......2.5W......5000 umhos....3W
6BL8.....5000 umhos......1.5W.......6200 umhos...1.7W
6EA8.....6400 umhos..... 3.1W..... 8500 umhos... 2.5W
-As you can see the ratings vary a bit- the 6GH8A output is more enthusiastic than the 6BL8. I read that the 6GH8 was developed for television and to avoid NOS branded for TV. I use an Amperex 6GH8 as substitute for the 6U8 in a McIntosh MR67 tuner as recommended by designer Modaferri. I can not distinguish the Amperex 6GH8A from the 6BL8 (ECF80) in construction.
The MR67 uses the 6BL8 as the "pre-pre"-amplifier tubes and I think the sound is fantastic. There is a premium 6BL8 (Euro des. ECF80) called either E80CF or 7643. Theses are gold pin, military and low noise, and ruggedised. I bought 6 brands of E80CF including the glamourous Valvo red label, pinched waist, but found that there are really only two designs- the Philips/Amperex/Valvo/Mullard with the heavy triangular getter support and the German one Telefunken/Siemens which are made by Telefunken. Of the two, I much prefer the construction quality and sound of the Philips one.
I liked the sound of the 6BL8 enough that a couple of years ago I looked around for a headphone amp that used it.
If fussing with an ST-70, you might benefit from visiting the Dynaco Doctor forum of this site:
http://www.audioasylum.com/forums/dynaco/bbs.html
I have a PAS 3 and ST70 which I hope to someday revive, though I imagine they will be redone more or less as stock- I'm not knowledgeable enough to hot rod anything,..
Cheers,
Bambi B
Follow Ups:
Bambi,
There are more replacement driver boards for the ST70 than you can shake a stick at. FWIW, I lean towards Triode Electronic's board populated with 2X EF86s and an ECC99. TE's board retains Hafler's pentode voltage amplifier DC coupled to "concertina" phase splitter topology, but uses in production types that have electrical performance superior to that of the sections found in an 7199.
Eli D.
I tried a couple of different 6bl8-ECF80 types in my Scott 222B.
When I tried a Valvo made E80CF, I never look for anything other than e80CF.
I have Mullard made ones and TFKN <> ones. Right now, I prefer the Valvo made ones.
I also use them in my Dynaco FM-3 tuner--same results.
Bob
"He (R.M. Nixon) was a foul caricature of himself, a man with no soul, no inner convictions, with the integrity of a hyena, and the style of a poison toad." H. S. Thompson
A McIntosh MR67 tube tuner (1964). The 6BL8 "Audio Amplifiers" are at the centre back- the two left of the back row in the photo above
Valvo E80CF red label, pinched waist, gold pin. You can just see the typical Philips double triangle getter support. All Philips, Amperex, Miniwatt, Mullard, and Valvo have this same design.
The Telefunken E80CF, which has the Telefunken construction of a wide, reinforced single bar getter support. Tubes labeled Telefunken and Siemens are both made by Telefunken
::::::::::::::::::::::
becketma,
I had the same experience- after trying the premium/military 6BL8- the E80CF/7643, I only looked to those. My impression was that the E80CF was more resolved and detailed, somewhat more energetic.
In 2005-6 the E80CF was inexpensive- the glamourous NOS Valvo red label pinched waist E80CF were $15 and many others were $5-8. The Telefunkens were more- $24 each, until I discovered that the Siemens are made by Telefunken- they have the diamond in the base- were $5 and $15. There's a clear demonstration that the Telefunken name makes the same tube cost more!
Checking German ebay.de- the best place to find the E80CF- I see prices have gone up, but these are still inexpensive compared to something like 12xx7's and 6DJ8 family stuff.
As the 6BL8 had not been made in nearly 30 years, I over-bought thinking I'd want enough to select from three types to fill the 6BL8 positions for two tube tuners for 30 years- and that would mean buying about 20 tubes. However, I bought twice that:
6BL8 /ECF80 /E80CF /7643 (2) TOTAL: 41
2- Telefunken E80CF- goldpin- NOS - [24
4- Philips Miniwatt ECF80-- Brazil- NOS -[5
4- Valvo E80CF Red lbl, pinch waist- gldpn–DE- NOS -[16
2- Philips SQ E80CF - Germany, gp-USED-TNOS -[8
4- Philips SQ / Mullard- E80CF- disc gtr- UK- NOS- [12
3- Siemens by Telefunken 7643- square gtr - gp- DE- NOS- [5
3- Amperex PQ E80CF-gp-Hamburg-db.gtr-NOS 64- [5
5- Siemens & H by Telefunken E80CF- gp- - NOS-[16
4- Amperex PQ 7643- gp- Hamburg- db.gtr s- NOS - [7
4- GE ECF80 -UK - NOS [2
2- RCA 6BL8- US - NOS [2
3- RCA ECF80 -France- NOS [2
1- Sylvania 6BL8- US [2
As I say, from the sound of the McIntosh MR67, I'd like to find a headphone preamp that can use the 6BL8/E80CF. Of course, a 6GH8A-based one would be the one.
Cheers,
Bambi B
I bought E80CFs after reading one of your post Bambi.
Unfortunately, I have a few Siemens labeled ones which were made by Valvo.
My experience is that one must ask whomever is selling Siemens who made them, and then tell them how they can tell if it was Valvo or TFKN <> .
Best from Tucson
Bob
"He (R.M. Nixon) was a foul caricature of himself, a man with no soul, no inner convictions, with the integrity of a hyena, and the style of a poison toad." H. S. Thompson
PHOTO: Some NOS Siemens and Halske E80CF, made by Telefunken
becketma,
While I did acquire a couple of RCA 6BL8, the European ones were all of only two designs. They were either the Philips configuration with the prominent double triangular getter supports or they were the Telefunken which looked more like 12xx7 and having a reinforced single post getter support. All the Philips brands: Philips, Miniwatt, Amperex, Valvo, and Mullard had the trianglular supports and the Telefunken and Siemens were made by Telefunken. I thought I had bought 6 different European 6BL8's, but actually I bought only two. A related surprise was that the NOS Amperex 6GH8A that I'm using as a substitute for the 6U8 in the McIntosh MR67 tuner MPX section was visually identical in every way to the original "McIntosh by Amperex" labeled 6BL8's.
Interesting too how the brands attached to the same tube had different prices- an Amperex or Mullard labeled tube cost more than a Valvo for example. This is the reason I buy Valvo- and on German Ebay- often- it's the same tooling as Amperex, but significantly less expensive as NOS.
I'm not surprised that there would also be Siemens made by Valvo- I assume by that you mean they have the "D" code to denote the Hamburg factory.
For some reason, I got special collectors' satisfaction with the Valvo pinched waist, gold pin E80CF- not only is the sound fantastic- it reminds me of the same kind of refined sound of the 7316, but it brings the glamour of some $200 Amperex E88CC- but for $20 instead.
One topic not mentioned before is that the 6BL8, 6U8, 6GH8 family seem to be very long-lived- 6AU6's too in this regard. Most of those types I have in late 50's to mid-60's gear- tuners/receivers- were still strong 40+ year old originals. The longevity must keep the price of NOS low as it does for so many tuner types. When retuning the MR67, I bought NOS Telefunken 6AB4, 6BE6, 6CS6, and so on for very little- $3-8. Premium 6AU6's like the 6136 (ruggedised) and 7543 (low hum) were inexpensive too.
As far as I know, a circuit that accommodates the 6GH8 should work- perhaps with a somewhat reduced output- with the E80CF and I'll continue to watch for a headphone amp based on the 6GH8. -I have all those E80CF's around!
Cheers,
Bambi B
Oh. I have a Mullard made by Valvo.
"He (R.M. Nixon) was a foul caricature of himself, a man with no soul, no inner convictions, with the integrity of a hyena, and the style of a poison toad." H. S. Thompson
nice looking tuner!
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