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What would it take to replace the 27 tube with a 26 in an existing 27/45 amp? Just wondering.
Follow Ups:
I guess the only direct substitute for the 27 is the 56, and it is the only 'garbage' tube I ever encountered.I believe I would rate the following 45 amps the following way but all are excellent.
1) 6sn7/26/45 a clear winner.
2) 717a/45 excellent sounding with the pentode driver.
3) 6sn7/27/45 a really great amp until the 26 came along.
I believe the second and third position are correct but I never did a direct comparison. first place is sewed up.
Hmmmmm . . . each to his own, and I'm usually philosophically aligned with njjohn. But lest the 56 be damned by no praise, I certainly don't consider it junk. My Loesch Triple-2A3's were inputted and driven by 56's by design, and substituting 27's in either position virtually destroyed the PRAT and hallucinatory magic of which those amps were capable. In fact, in my zeal to find the "right" 27, I amassed a huge collection including mesh 227 and 327's, none of which were acceptable in that configuration. Damned if those tubes don't make great line stages though, particularly the meshies, which sound majestic by comparison to other 6SN7 precursors. But 56's junk? I think not. Not nearly.
> My Loesch Triple-2A3's were inputted and driven by 56's by design <I would love to be able to see a schematic and parts list for that amp. I would like to see what made this combo work.
Kurt, I never was provided, nor did I develop, a schematic of those amps. And I also recollect that John Wiesner, who built 'em, wasn't crazy about releasing his schematic. Top quality parts though: vintage Hammond iron, Black Gate WKZ's, Mills non-inductives, Electra-Print OPT's, Rel-Cap teflons, etc., immaculate workmanship. The amps had a stop-you-in-your-tracks tone and gut-wrenching immediacy. Listening to 'em, on a good night, was an event. Yes, they were, horror of horrors, paralleled 2A3's; but by some large margin, best amps I've ever owned.Regards,
I guess the only direct substitute for the 27 is the 56, and it is the only 'garbage' tube I ever encountered.>I have quite a few of these I haven't yet used for a project. I thought people spoke highly of them - don't they sound very similar to the 76? Why garbage?
The 56 is bright and brittle compared to the 27. If you need a bit more HF energy then maybe the 56 would sound better, but I have not found any real case where the 56 bettered the 27, except by having a little extra gain. I never heard the 76, and discounted its use after the 56/27 comparison I made. Maybe the 56 can overcome a really sluggish oil cap, but you're better off with a good cap and a 27.
Thanks for that - gives me an idea what to look forward to.
is there a public schematic for this amp?
Thanks in advance
I don't think there is. There are seperate schematics for the 6sn7, 26, and 45.The builder of the amps passed away and I believe he does have a schematic of the 26 amp but I have to wait some time before the family is ready to help out.
And I can recommend it with the vintage opts that he used because there is an interaction between the design and the opts. It may be as good with other opts but I can't vouch for it.
x
I guess i shouldn't have generalized so much about the 56. i believe I tried to substitute it in only one amp, and as described it has more gain than a 27 but it did not sound good. I think I had purchased a few of them on ebay, and I thought i wasted my money on this tube. But perhaps nothing can be discounted the way I did it.The opts are particular vintage Hammond opts. Some are in amps built be Webster and I think they are in what are called tone cabinets which are speaker cabinets (with an amplifier) which were built specifically for organ amps in the 1940's. I believe they were 2a3 amps. The other ones were bigger opts in larger chasses and I'm not sure what they were in. the latter were built in the 50's. I think the first one has 60 dc resistance, and the latter ones had 120 dc resistance. I think the latter ones may have been in 6v6 amps and maybe other kinds too. They were also organ related amps.
The opts are push-pull but they are used in single ended operation which was also done by Korneff with Sansui opts in his early amps.
Among IDHT's, the 27 is probably my favorite. But the best ones are the globe mesh plates. The move to a 26 here is not as big as it should seem, going to DHT, especially since that will probably be DC heated. And a DC heated 27 won't matter much to the sound compared to AC since it is indirectly heated, except for less hum and buzz.If you haven't tried the old globe mesh plate 27's, I wouldn't move to 26 yet. If you get significant hum from the globe 27's, then you need to build a metal shield around it and DC heat it. I have a 27 line stage that required both of these measures. It was the best line stage I had before I moved to a TVC. The extra steps to get it quiet really paid off.
That said, I do think the DHT drivers sound better. I think the 01A is the best sounding driver I've had in my system. But it is a lot of effort to change over.
But also, finding a good pair of RCA globe meshplate 27's is not all that easy either. Some hum more than others. The problem with this particular IDHT is that they hadn't yet figured out the concept of twisting the filament for hum cancellation inside the tube. So hum it does a bit on those early versions.
Quite a lot. Changing from a 5-pin socket to a 6-pin will be the easiest change. While the mu of the tubes is similar the 26 may require you to drop the B+ a bit. The real issue is going to be figuring out what you can live with as a filament supply for the 26. AC on the 26’s filament will probably give you objectionable hum. You could use high-frequency AC but then the complexity of tube swap grows. Battery DC filaments are probably the easiest of your options if you don’t mind the hassle of using rechargeable batteries. Getting rectified DC to sound good could be as complicated as high-freq AC. This is not a plug and play tube swap.
Matt
Base of 27 is:
1 - fil
2 - anode/plate
3 - grid
4 - cathode
5 - filBase of 46 in triode is
1 - fil
2 - anode/plate
3 - grid
4 - grid 2
5 - filSo to switch from 27 to 46 you would presumably disconnect the cathode resistor from pin 4 and connect it up to the centre point of two resistors going to pins 1 and 5. You would then connect pin 4 to pin 2. You would have to work out the new cathode resistor value. Since the mu of this is lower, it would be quieter. Presumably it would work with AC as above, provided your 2.5v filament supply feeds just the one tube and not several.
For 1624 the mu is similar. Pinout is:
Topcap - anode/plate
1 - fil
2 - grid 2
3 - grid 1
4 - NC
5 - fil
So here you need to run the plate lead up to a topcap, connect the cathode as with the 46 and connect pin 2 to the topcap. In this case the filament current is 2.5v at 2amp, so you need to check that your filament supply can deal with this before proceeding.I hope I have all the above correct - if it is then these two tubes may be worth trying, provided you know what you are doing and can do all the calculations for cathode resistor value etc. In neither case is it a plug and play option, but in both cases the tube base and filament voltage is the same. Like I say, you need an independent filament supply to each tube since they are now directly heated.
thanks
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Boo!
The 1626 is 12v heaters and octal, but its sound has been likened to the 45 in some postings.
The 47 should be same base as 46, though operating conditions would vary. Again, as with the 27 and 46, flament is 2.5v at 1.75amp.The 49 is yet another UX5 base, 2v filaments with a filament current of 120mA, so you'd need resistors or something to bring the voltage down from 2.5v to 2v. Pinout is as 46 or 47.
The 24a is a theoretical possibility, though I doubt if it would sound good enough to be worth trying. also UX5 base, 2.5v at 1.75A filaments.
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