6BM8??? Whazzat?

[GordonW]

Hey, I've run across a piece of new gear, that uses 6BM8 output tubes. Now, I've never seen those before, and they're not in any of my RCA tube reference guides or the old Parts Connection/Sonic Frontiers lookup guide.

So, anyone care to fill me in on what this tube is? Likes, dislikes? Specs? Parameters? Tube-rolling opportunities?

Thanks!

Regards,
Gordon.

[timoteus]

The 6BM8 has a triode driver section and a pentode output section so you can make an amp with one tube per channel. There are a lot of fans of this tube in Asia and even 6BM8 clubs over there. I think they have also been building these amps in some kind of "Super Triode " configuration. Most of the 6BM8 sites are in japanese, but there are some nice pics to look at.

[Thatch_Ear]

The pentode section is simular in output to a 6BQ5 in PP and 3.5 watts SE Class A. US brand I have seen is RCA, French Mazda is supposed to be good and I have a number of labeled Westinghouse made in Slovakia that are good. 6BM8s were popular in Japanese amps and were sold under the name Monarch, Calrad and Realistic but all probably came from same factory and look in build very much like Kenwood gear of that time.
There is a fairly recent design I believe of Japanese origin where a dual triode is used for amplification and the triode section of the 6BM8 is used as a voltage regulator. Dennis Boyle of Chimera Labs is in the process of building a prototype mono block with the power supply and OPT from a Mullard 3.3 which is a SE 6BQ5 circuit. One odd thing about this is that there is an audio choke of 200 Henries in the circuit. Whether this is something developed by Dennis and his transformer winder in England as a variation of the Japanese circuit, I don't know. I hope to see and hear the prototype amp soon, maybe to have a pair to take to Austin in May.

[Thatch_Ear]

Super Triode Connection

[Thatch_Ear]

The original Hirosha Uda UTC amp......... the famous cookie can amplifier.

[Thatch_Ear]

There are now many variations of this circuit, but basically from what I understand the STC 6BM8 gives you the power of a SE 6BQ5 but the circuit is much more linear, especially in the lower levels making for superior bass response. Well it will be interesting to review these amps when built.
Unfortunatly the Mullard 3.3s were taken apart for the transformers so a direct comparison of the STC 6BM8 and a comparable SE 6BQ5 won't be done.

[mhardy6647]

6BM8 was quite popular in Japanese tube receivers and amps in the ol' days (1960's). Also used in TV's I suspect. It is definitely in one of my RCA tube manuals, but I can't recall which (probably the RC-30, from the early 1970's).

The little S-5 Electronics amp uses 11BM8's (presumably the same tube with 11V filaments) for driver and output duties (4 tubes in toto for a stereo push-pull amp).

[RocknRoll]

Here you go fellow tube heads - it is in the RC 25 tube manual. 6BM8/ECL82. :)

[cruisaire]

Gordon,

Was that in the Delmonico I saw?