Petertub,
EL34 filament to cathode 100V max.
7199 filament to cathode 100VDC, 200V peak (both triode and pentode).
The 390k 82k divider gives about 75V to the filament.
This is not as much of a band-aid, as it is a disinfectant.
All solutions have tradeoffs, and . . .
"ALL Generalizations Have Exceptions"
EL34 filament to cathode 100V max.
7199 filament to cathode 100VDC, 200V peak (both triode and pentode).
The 390k 82k divider gives about 75V to the filament.
This is not as much of a band-aid, as it is a disinfectant.
All solutions have tradeoffs, and . . .
"ALL Generalizations Have Exceptions"
The 6EU7 sounds a lot like the 6N2P-EV with a different pin-out?
“-YeV" (Russian: "-ЕВ") added after 6N2P (i.e. "6Н2П-ЕВ") signifies that this variant of the 6N2P has extended service life and low noise and microphonics.
They have the shield, 6.3V, mu of 100, pull a bit more current than your average 12ax7. Tend to be slightly less gain than published but heck at their going rate you could buy a box and keep the best.
People have called this tube all sorts of names like a 6DJ8 replacement but in practice I’ve found them more similar to a low noise, high reliability 6ax7.
I think it could be a good choice given your conundrum.
“-YeV" (Russian: "-ЕВ") added after 6N2P (i.e. "6Н2П-ЕВ") signifies that this variant of the 6N2P has extended service life and low noise and microphonics.
They have the shield, 6.3V, mu of 100, pull a bit more current than your average 12ax7. Tend to be slightly less gain than published but heck at their going rate you could buy a box and keep the best.
People have called this tube all sorts of names like a 6DJ8 replacement but in practice I’ve found them more similar to a low noise, high reliability 6ax7.
I think it could be a good choice given your conundrum.
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Hi 6A3sUMMER,
So was I. I should try and dig up the manual for that old beast.
Hi spaceistheplace,
Where does one find a 6N2P-EV? That and the specs? It does sound promising. The only thing that kept me from rebuilding it so far (I've had it for >20 years, paid too much for it too) was the cost of the tubes. As I recall, I opened the top, counted and checked the tubes and closed it back up once I realised the costs in tubes alone. I'd love to see this one working again at some point. I also have an ancient HP square wave generator, 211? I'll have to look. That's another one to restore. That one is HUGE!
-Chris
So was I. I should try and dig up the manual for that old beast.
Hi spaceistheplace,
Where does one find a 6N2P-EV? That and the specs? It does sound promising. The only thing that kept me from rebuilding it so far (I've had it for >20 years, paid too much for it too) was the cost of the tubes. As I recall, I opened the top, counted and checked the tubes and closed it back up once I realised the costs in tubes alone. I'd love to see this one working again at some point. I also have an ancient HP square wave generator, 211? I'll have to look. That's another one to restore. That one is HUGE!
-Chris
All over eBay: 6N2P-EV Lot of 100 pcs. NOS Voskhod Rocket | eBay
100 for less than a single Telefunken 12ax7.
Datasheet: http://www.mif.pg.gda.pl/homepages/frank/sheets/112/6/6N2PEV.pdf
100 for less than a single Telefunken 12ax7.
Datasheet: http://www.mif.pg.gda.pl/homepages/frank/sheets/112/6/6N2PEV.pdf
PS probably already mentioned but 6U8A/ECF82 has become the de facto 7199 replacement.
There are other various solutions including using other tubes, multiple tubes etc. but I think you can probably get by just fine with this one with some circuit alterations.
Between Keysight and the Hp archive project just about every old schematic for that gear is easily accessible online:
https://www.keysight.com/upload/cmc_upload/All/211A_Final.pdf
http://hparchive.com/Manuals/HP-203A-Manual-sn425.pdf
http://literature.cdn.keysight.com/litweb/pdf/00203-90000.pdf
(Took a wild guess on your generator model)
There are other various solutions including using other tubes, multiple tubes etc. but I think you can probably get by just fine with this one with some circuit alterations.
Between Keysight and the Hp archive project just about every old schematic for that gear is easily accessible online:
https://www.keysight.com/upload/cmc_upload/All/211A_Final.pdf
http://hparchive.com/Manuals/HP-203A-Manual-sn425.pdf
http://literature.cdn.keysight.com/litweb/pdf/00203-90000.pdf
(Took a wild guess on your generator model)
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See above for my edits / further info.
Yes there’s a ton of different possibilities.
Of course, you could buy a lot of things with what those smooth plate telefunkens are going for these days. Crazy..... Will only get worse from here.
NOS / NIB Telefunken ECC83 / 12AX7 Tube Smooth Plate Western Germany Berlin | eBay
Yes there’s a ton of different possibilities.
Of course, you could buy a lot of things with what those smooth plate telefunkens are going for these days. Crazy..... Will only get worse from here.
NOS / NIB Telefunken ECC83 / 12AX7 Tube Smooth Plate Western Germany Berlin | eBay
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Hi spaceistheplace,
Thanks again.
I normally buy the Electroharmonix 12AX7EH, and have for many years. They are quiet and pretty darned consistent. They go into repairs and anything I design. I wish someone would pay me the going prices for all my NOS tubes that I can replace with Electroharmonix tubes. That would make me a very happy fella.
-Chris
Thanks again.
I normally buy the Electroharmonix 12AX7EH, and have for many years. They are quiet and pretty darned consistent. They go into repairs and anything I design. I wish someone would pay me the going prices for all my NOS tubes that I can replace with Electroharmonix tubes. That would make me a very happy fella.
-Chris
This is correct.
The cathode<>filament isolation is far from perfect. Higher voltages then
a few volts will increase the risk of breakdown or leakage.
The best solution would be to elevate the filement for the cathodyne only, leaving the other filaments within a few volts from their cathodes. This is not possible with "combination tubes" like 7199 where the sections share filament.
Your suggestion is a fair tradeoff, but it is still a compromise .
Morgan Jones for example. He suggests doing exactly this in the 3rd edition of his Valve Amplifiers book. His argument: It is much easier to select two identical triodes from a batch of 6J5's than to find a 6SN7 with identical triodes in a resonable number of tubes.
Is this the European ECC808? Well, in this case you're quite right. As any tube type that was developed when tubes' use already had begun to decrease in consumer equipment (remember EL503, ECL86 etc.), these are scarce and really expensive nowadays.
Best regards!
Another vote for the Triode Electronics replacement board for the ST70 that uses a EF86 input tube and a 12AU7/12BH7 or other variant for the split load inverter. Years ago, when I replaced my stock board with the EF86/12AU7 board, my ST70 never sounded better. Plus, being able to select the best sounding input tube and best sounding inverter tube is a real advantage.
Try an ECC99, which pins out the same as the 12AU7 & 12BH7, for the phase inverters. The requisite additional heater current is present and the ECC99's gm is considerably larger than that of the other 2. A "concertina" phase splitter is a "tricked out" voltage follower and high transconductance makes for a good voltage follower.
If I still had a ST70, I would try the ECC99 but I haven't had a Dyna for a long time now. I do recall that I preferred the sound quality of a NOS 12AU7 over an EH 12BH7 on my Triode Electronics board. I don't recall which brand of 12AU7 I liked better. Unfortunately I only had the EH version of the 12BH7 so it wasn't an entirely fair comparison.
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