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12.10.199.12
In Reply to: RE: This looks like the place to be for Sherwood owners posted by Bamboo Pentagon on April 19, 2015 at 18:28:18
The 7199 has gone the way of the Dodo; it's extinct. The best substitute (with rewired sockets) is the 6GH8, but that type is out of production and supplies are dwindling. AAMOF, all suitable pentode/triode types, like the 6U8 and 6BL8, are headed towards extinction too.I suggest you buy several sets of power section small signal tubes, while it's still possible. A 2 tube set does not have to be "matched", but should come from a single plant and a single production run. Even that low level of selectivity may be difficult to achieve, given the dwindling supply situation.
There is hope, for the time when suitable pentode/triode tubes cease to be available. The excellent EF86 small signal pentode is in production and fits 9 pin mini sockets. OK, the voltage amplifier is taken care of, but the "concertina" phase splitter remains. Adding an additional 9 pin socket to the very limited space is not particularly feasible. However, "sand" rides to the rescue. The ZVN0545A TO92 case MOSFET is space efficient and it makes a nice, highly transparent, DC coupled "concertina" phase splitter.
If you are going to own "vintage" tube equipment, some technical skills are necessary. If you lack such skills and are unwilling to acquire them, you'd better have a very, very, "healthy" bank balance.
edit: fixed "typo"
Eli D.
Edits: 04/20/15Follow Ups:
Sovtek used to make an O.K. 7199 equivalent. Is it that this tube is not used in guitar amps?
I like your EF86/ ZVN0545A TO92 case MOSFET solution. Will it drive a pair of 6550's?
Dave
The Russian 7199 "equivalent" is out of production and, as you surmised, New Sensor IS guitar amp oriented.
The EF86/ZVN0545A combo could be OK, with full pentode mode KT88/6550 "finals". I have my doubts about UL mode. As there are several satisfactory replacement driver boards for Dyna MK3s, the issue is (IMO) moot.
JMO, Dyna/Scott/Sherwood style small signal circuitry is at its limit with EL34 class tubes. I definitely prefer Mullard and Williamson style circuitry, when the 6L6 family and KT88s are the "finals".
Like the 12AX7, the EF86 is a wimp that "can't fight its way out of a wet paper bag". The capacitances of the ZVN0545A are tiny and the wimpy types drive the little FET quite easily. I'm not comfortable DC coupling something like an IRFBC20 to the wimpy types.
Eli D.
Yeah, the 7199 issue is definitely a concern with these. I have a stock of 4 strong ones in addition to what I have running in the amp right now. Couldn't hurt to stock up on some equivalents in case I need them. The 6gh8a's look to be plentiful and inexpensive...for now.
I have 4 strong 7199's as well as these nifty little adapters.
There is no need to rewire your amp to accommodate the 6GH8A or 6U8A. Just plug 'em in and play music.
Meat; It's the right thing to do. Romans 14:2
... and while I guess you could say they "worked," the results were FAR from good. Nothing wrong with the new tubes or the adapters that I can find, so it was probably just that use that was inappropriate. I have an S-5000 that is waiting on some transformer work, so I've got time and space to do any rewires, but I may wait and try the adapters before committing to a new tube config. I've been laying up 7199s here and there for a few years, I have 3-4 sets of NOS, but I believe the Sherwood runs them pretty hard, so I'm keeping an eye out for alternatives in case I get tired of shelling out $20+ per tube, like the last set.
you didn't make them yourself? Thanks.
I picked mine up on Ebay.
Just search 7199 adapters.
Meat; It's the right thing to do. Romans 14:2
nt
Very nice! Also have an S-2200, but without the MPX adaptor. I recapped it last year and replaced the dual-concentric volume pot with individual pots. Mine was so corroded that repeated DeOxit treatments couldn't bring it back. All original Sherwood brand tubes in mine!
Before I get scolded for stacking--I'm using two PC fans connected to a wall wart to exhaust hot air from the S-5000's power tube chimney and from the case. The amp stays cool to the touch and the tuner doesn't seem to suffer from any drift.
No MPX adapter = no or very little problem. :> ) DIYer extraordinaire S. Bench has provided us with a nice IC based design. The only potential real trouble is the drive capability of the discriminator and a JFET buffer will dispose of that.
Eli D.
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