Mullard 6L6GT

[Paul P]

I recently acquired a Heathkit 400v power supply and
when I opened it I up found these :

[ATTACH]35[/ATTACH]

Net wisdom says that Mullard never made 6L6GTs and
that IEC (in New York ?) used the Mullard name at some
point. These do say IEC Mullard. However, they
are also marked GT BRITAIN, though not "made in" GB.

These look to be in good condition, the power supply
seems to have been little used, if at all. Should
I remove them and keep them for my dream amp (yet to
be built) or should I leave them where they are ?
Would modern day 6L6GTs work as well in this power
supply ?

According to a Heathkit site the power supply (IP-17)
was offered between 1968 and 1977 which makes it about
30 years old. Should I re-cap the thing or leave it
alone ? It's pretty much new inside, but I plan to
use it quite a bit.

Paul

( They're not for sale )

[Rob Mercure]

Hey Paul,

Unfortunately your pic isn't lit well enough - and could use a lighter background - so I can't easily guess at the tube's make. But Mullard factory tubes have a two "row" of a couple of letters/numbers that identify the date, factory, and the tube type - usually near the base of the tubes. Also the "Mullard" stamp looks a bit "off" but I can't really tell that much from the photo. If you really want a specific identity the fanatics over at Tube Asylum could probably help:
http://www.audioasylum.com/audio/tubes/bbs.html

If you're going to use the PS I would definitely replace all of the electrolytics and measure the power resistors. Does it use a gas discharge tube (OA3, etc.) as a voltage reference?

If you like the tubes I'd reserve them for audio - you might want to "audition" them in a known 6L6 circuit - and use the least expensive replacement you can find for the PS. This may be a perfect use for the ubiquitous Sovwrek "5881s."

Rob

[Enzo]

The 6L6s are the regulators. If there are glow tube regulators, they would either be for a reference or for secondary voltage reg. No reason why absolutely ANY 6L6 glass tube wouldn't work. Even worn out ones with no tone left.

As to throwing all new caps in there sight unseen, this thing is at the what is there to lose stage, so whu not fire it up and find out what caps need replacing or not? When I rebuild jukebox amps of that era, I usually find the electrolytics are still OK, it is the coupling caps that are all gone leaky.

Even if these are not fancy tubes, why not save them? Whatever they are, they will be different from anything else you have.

On the other hand if this unit has selenium rectifiers, I WOULD replace those.

[dai h.]

I would guess those were either Japanese or U.S. made. There were 6V6, and a 6L6G (Visseaux of France) from Europe but seemingly none or very little 6L6GCs (which is what those look like). Russian ones also (the one that is more of a 6L6GA or B, and the old "5881"--but that doesn't look like the American one) but neither look like that.

[Satamax]

I would guess those were either Japanese or U.S. made. There were 6V6, and a 6L6G (Visseaux of France) from Europe but seemingly none or very little 6L6GCs (which is what those look like). Russian ones also (the one that is more of a 6L6GA or B, and the old "5881"--but that doesn't look like the American one) but neither look like that.

Hi everybody!

Dai, there's also Fivre in Italy who made some nice 6V6.

Bye.

Max.

[dai h.]

hi Max!

yes, I think I've seen those as well. All the W.Europen tubes look very well constructed to where they look physically beautiful (or at least it seems that way). Maybe it was the dominance of Dutch Philips (their EL34) was why there don't seem to be any W.Euro 6L6GCs? In Japan there were both Euro and American types. I think Toshiba, Hitachi, and NEC made GCs and EL34s. Matsushita (partly owned by Philips) and Ten, EL34s.

[Euthymia]

Nice find (the power supply)

I bought an IP-17 at a ham swap a couple of years ago and, yes, my eyes bulged when I took a look at the tubes.

My tube dealer friend brought me back to earth by informing me that the Mullard factory never produced a 6L6 and that they were probably of Japanese manufacture.

So, while they are interesting as a curiosity, they are not worth the king's ransom one might expect.

I replaced them with a pair of scorched wafer-base Sovtek 5881's I had pulled from a repair amp.

That power supply is a dream come true for anyone experimenting with tube amp designs, and/or doing repairs. Heck, you could make your own tube tester with not too many more parts.

Mine was cheap, probably because it came in the "decaying Barbie doll" rubbery tan finish.

[Paul P]

Thanks for the replies. I've been mostly away from my computer
for the last couple of months (not any more) so didn't notice the
replies until recently. When I get a chance I'll take the tubes out
again and try to get some better pictures.

I paid quite a bit more than 'cheap' for the IP-17 mostly because
I want to do a lot of experimenting to really learn what's going on,
and partly because the description was "in mint as new condition".
Well it was, overall, except for the really thick brush-applied flat
black paint to the chassis and the magic marker blackened bezel
around the front panel. Why would anyone do such a thing... I
stripped it down and now it's a gorgeous sky blue with a grey bezel.

I've bought replacement caps for it (Mallorys) but I'll first check out
the ones in there on my Sprague TO-6A tester that I happened
across at a flea market this summer for 30$ (once I replace the
caps inside that as well).

I seem to have slid down a slippery slope of acquiring test gear.
Still haven't started building anything but I'm getting closer...