PL504 SET

[sorenj07]

Anyone ever considered using a 6GB5/PL500/EL504/PL504 type tube in triode mode?

http://tdsl.duncanamps.com/show.php?des=6GB5
http://tdsl.duncanamps.com/pdf/pl504.pdf


those curves are pretty, and the tubes are available. at full 17W dissipation i figure that an output power of 4W ought be reasonable to expect.

B+ of 210V, cathode bias at 30V 80mA into a 1.5K load. i have no clue if that would sound good. during transients current might momentarily hop up to 175mA per tube! biiig B+ reservoir capacitors and a beefy PT good for 300mA or so are in order, i think.

any takers? i'm sure that there's an antek toroid out there that's good for the job. finding the right OPT that can take that much current might be tough though, and needing a second voltage supply for the input stages might also be a hassle. enough to justify just getting a couple 300B's ?

[TerrySmith]

This might just be a good "sweep tube" to try. It's one of the few with decent screen ratings.

I think my plinker stash includes one each 6GB5, 18GB5. and a 27GB5. All look to be rebranded Mullards, as this is a foreign type.

[EWBrown]

RCA 6GB5 data sheet here:

http://frank.pocnet.net/sheets/049/6/6GB5.pdf

The 1.5K plate load sounds like a good match for the One Electron UBT-1,
these have a 1.6K primary, 160 mA capability. THese are listed on the AES www.tubesandmore.com site.


These and the somewhat rarer 6KG6 EL509 / PL509 (not to be confused with 6GK6) are both interesting "hefty" power tubes.

/ed B in NH

[sorenj07]

Seems like it could be very cool. I'm sure that an Antek toroid would work excellently, especially for "stacking" the secondaries to feed the higher B+ of the driver stages..

As always I try to be very budget conscious, and it doesn't make much sense to me to blow $180 on OPT's. It might be worth asking Edcor to wind some custom ones good for 10W 20-20 or so, at 1.5K. Probably wouldn't be that expensive. Has anyone used this thing in UL?

Another random question: Does anyone have a curve tracer? I still have some 6P9 (6AG7) and 5763 tubes I'd love to see triode/UL curves for...

[EWBrown]

Finding budget OPTs in the 1.5K impedance range may be problematical, even the 125ESE would be at the upper edge of its limitations with this tube...

Edcor could probably cook up something appropriate, I just hope that their small lot custom jobs are still reasonably priced.

Occasionally AES drops the price on the UBT-1s down to 79.95, but then that's still quite a "chunk of change" for a pair of them, especially on a student's budget...

One of the guys in NNETG really likes the 6KN6 and 42KN6, these sweep tubes contain two parallel BPTs inside the envelope and he says that they are very linear in triode service. He is working up a design for an SET using these, for a friend of his at his workplace.
He has also talked about a Japanese transformer company called "Soft Tone" - or softone who produce good iron at "reasonable" prices, but then he considers Magnequest as "middle of the road" iron...

good luck, it sounds like an interesting project.

/ed B in NH

[Francois_G]

Anyone ever considered using a 6GB5/PL500/EL504/PL504 type tube in triode mode?
<snip>
those curves are pretty, and the tubes are available. at full 17W dissipation i figure that an output power of 4W ought be reasonable to expect.
?

I have a nice stash of these guys, acquired after reading Richard Berglund's article on the use of sweep tubes in "Glass Audio". The article was published quite a while ago, before it became ExpressAudio.

He directly substituted a 6GB5 in place of an 2A3, without changes (except to adjust for bias current) and apparently found it to perform very well. Actually he measured less distortion using the 6GB5! He also tested a bunch of other sweep tubes and compared them to 6550, EL34 and 6L6 -- in most of the distortion tests the sweep tube outperformed the "audio tube"

The 6GB5 is unique among sweep tubes to have a screen supply and plate B+ at the same voltage.

Francois

[sorenj07]

cool! have you done anything with them yet?