next project: rebuild using fisher 500c trannies

[SY]

The 6BG6 project is still a work-in-process, in the proto stage I demonstrated in the "Ugly Prototypes Contest" thread. I'm actually using EL37s in the Eico right now for listening; I think they're fantastic for this app, but they're my last set and finding/paying for replacements is well past my margin of pain. That's why getting the 6BG6s to work in this application is a high priority When I'm done (I still have to check it out with some 4300 ohm trannies), I'll post the results. These tubes are really cheap, but might turn out to be something really special.

[fdegrove]

Hi,

These tubes are really cheap, but might turn out to be something really special.

Once had a couple of Westrex monoblocks using 6BG6s.
It's a very tough tube, virtually indestructable, sounded good too.

The Westrexs' sounded a little dated, rather darkish, but still had good bass.
It's hard to tell tell much of the qualities are due to the tube itself but it certainly is well worth investigating.

Cheers,

[zobsky]

according to some info on the web ( eg http://groups.google.com/groups?q=6b...inc.com&rnum=9 ), the 6bg6 and the 807 are near equivalents except for the base and also be used in 6l6 based designs.

[SY]

It depends on the 6BG6. Some of the ones I have on hand do indeed look like 807s, albeit with smaller plate structures (20W Pd). The ones I'm checking out now are claimed to be rebased 7027/7581 types (30w Pd), and sure look that way. I'll take some comparative photos later and post them. BTW, they listed as NOS at $6 a pop.

[Jax]

I could swear I had a couple of 6BG6 but it wasn't. It's 6CD6, same shape as 807 but the innards are the weirdest I have seen. 2 cathodes, 2 grids, 2 screens, one shared beam former and one shared plate. No idea what they were for.

[zobsky]

i think i'll take a chance on the 6BG6 (a little more power than the 807) since there is not much to lose even if they don't turn out well. they should work with the fisher trannies. i'll postpone my DHT 2A3 push pull plans till after I have had a chance to see how these things work (plan to order tomorrow). I'll document the build in this thread. If things go well, I should be able to build this amp for $150 to $200 (if I don't use exotic IT iron) which should be an amazing value if it sounds good.

may look at the 807 schematics mentioned in this thread

everyone on this thread has suggested to stay away from triode operation on the 807, .. and i assume the same for the 6bG6 too??, .. but why??? , .. a matter of sound ??

so far,
topology: push pull
circuit: to be decided
output iron: fisher 500C / 800C
tubes: 6bG6
input iron: to be scrounged depending on the circuit to use.
driver tubes: to be decided

i'll search around on the www and maybe look at the tube curves and post back when i have new info.

thanks,

[Brett]

Originally posted by zobsky
the idea of using interstage transformer as a phase splitter in the ralph PP appeals to me. in this regard:
a. how expensive are lundahl ITs, .. couldn't get an idea off their web page but i'm estimating $150 or so per pair.

Been away again and have just seen your post. Lundahl prices in the US can be found here.
http://hometown.aol.com/kevinc927/my...business1.html

I beleive the 1660 are the best for this application, but email Kevin and ask. Very knowledgable and helpful.

[zobsky]

thanks for the pricing info on lundahl ITs,

as i progress towards defining the components in this project, ...
i want to question / understand the differences and expected advantages / disadvantages in expected performance / sound between an IT vs coupling cap, ..but wanted to read up a little more before i can construct intelligent questions on this topic.

oops, too late, i already asked

[zobsky]

BTW, .... wondering about these line matching transformers (ridiculously low price)

http://www.edcorusa.com/magnetics/au...wsm10k-10k.htm

mentioned here
http://boozhoundlabs.com/edcor/

would they work? perhaps, but how well? if not as an IT, it might be possible to use it as a phase splitter on the input itself.

also, why might input stage iron be a better choice than IT iron (SY) ?

[SY]

I prefer keeping voltage swings and currents through the iron as low as possible. So, 1V (more or less) is more appealing than 50V (more or less).

And a well-chosen input transformer gives you really good common-mode noise rejection. I'm using the Jensen JT-11-P1 (thanks to Steve Eddy for talking me into trying them), and it works as advertised, does a fine job producing a balanced signal, has good bandwidth and very low distortion, and is relatively inexpensive. So doing it this way kills two birds with one stone. The disadvantage is that it works best with a 10K load, which is a bit low for most tube preamps to drive. OTOH, Jensen claims that an RC snubber will allow higher load resistances; haven't tried that yet, but it makes sense.