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"
anatech,
Sorry for your large need for 7199s and 6EU7 for the HP generator.
I am kind of surprised that HP used the 7199s.
Sorry for your large need for 7199s and 6EU7 for the HP generator.
I am kind of surprised that HP used the 7199s.
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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Thanks.
I don't buy 12AX7A's anywhere close to that price, wow! I'll see if there are lower quantities available. Thanks again.
Okay, I found a group 0f 10 to try.
-Chris
I don't buy 12AX7A's anywhere close to that price, wow! I'll see if there are lower quantities available. Thanks again.
Okay, I found a group 0f 10 to try.
-Chris
Hi spaceistheplace,
I think I already have that one, but thanks. I'll look for the MPX generator tomorrow once I get the model number off it.
-Chris
I think I already have that one, but thanks. I'll look for the MPX generator tomorrow once I get the model number off it.
-Chris
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
The Mesa Boogie SPAX7A has been my go-to “secret cheap 12ax7 tube” for repairs and new builds for a while. (especially V1 where it’s been undefeated)
But always looking for new options.I’ll try the EHs. Thanks for the tip.
But always looking for new options.I’ll try the EHs. Thanks for the tip.
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This is correct.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"
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 .
Who would use 2 6J5 tubes instead of 1 6SN7?
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.
The 6EU7 was an excellent choice back then, but it is a killer for my pocket book today. The 6EU7 was an improved 12AX7A with a different pinout for reduced hum pickup. It also had a shield between the two sections like the 6922 does. What's not to like about an improved 12AX7A?
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.
Hi Kay,
Hi Eli,
Best, Chris
Yes, that is very true. Even with some current manufacture tubes where they have processes under better control these days.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.
I don't know off-hand.Is this the European ECC808?
Hi Eli,
Sounds intriguing. Does it have a North American equivalent?Try an ECC99
Best, Chris
@ anatech: In the meantime I did some research and found out that 6EU7 isn't ECC808. Their data are almost the same, but the pinouts are very different, with the heaters very uncommonly tied to pins 1 and 2 in the 6EU7.
The ECC808's cross reference is 6KX8.
Best regards!
The ECC808's cross reference is 6KX8.
Best regards!
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