Audio Asylum Thread Printer

Get a view of an entire thread on one page

FAQ / News / Events

Tubes Asylum

RE: DB110G (Bogen) 1950s.

81.185.161.248

ivan_terrible

In Reply to: RE: DB110G (Bogen) 1950s. posted by ivan_terrible on December 26, 2023 at 11:20:29

"I won't use self bias (cathode bias) in any push-pull amplifier".

Well that was what came with the amp, and for that matter, a large proportion of the 60s amps.
They do say, beam tetrodes only sound good when they are about to melt.
I reckon that's good advice.

I have run quite a lot of the old 6L6oids ie. 807/KT8
They do give best performance/lowest distortion when the anodes are glowing red in bits, or well over 85% of max Pa at idle.

The 6V6 (7408) Westinghouse valves are clearly better.
They look almost identical to the 7591, a far higher gain more linear component than the ancient 6V6 or the miniaturised 6BW6 and their clones.

Talking of this...I bought a load of 6BW6 cheap cos nobody wants them.
In the space for ONE octal (or 7C5 Loctal) you can fit a pair of 6BW6 so as to run PPP.
Actually quite a nice idea if that floats your boat.

Follow Ups:

RE: DB110G (Bogen) 1950s. - Triode_Kingdom 20:32:51 12/27/23 (1)
I'm a big fan of the 6V6, but being a cheapskate, I've been collecting sleeves of NOS 12V6 for a long time. Recently replaced the well-worn 7408s in my small dual-mono SEP with 12V Sylvania chrome domes. They're really superb. I also have a large stock of 6P3S-E and a couple dozen NOS 5881, so my mid-power DIY plans revolve mostly around 6L6 pentode designs. Those 6BW6s look interesting. I bought a large quantity of little 5686 8.5W pentodes some time ago. I'm using them in triode in a preamp project now, and hoping to use them in pentode push-pull in a future guitar amplifier. So many tubes, so little time!
- RE: DB110G (Bogen) 1950s. - ivan_terrible 01:32:15 12/28/23 (0)
  Of course you can carry on collecting stuff for ever, but it's of little use.
  Currently the loctal 7C5 go for peanuts.
  I bought a large qty of Mcmurdo loctals to put them in if needed.
  The 6L6 types can also be had for peanuts in loctal using the 254/255M series from STC - UK mil spec made.
  
  I managed to start up a pile of them making an adaptor from UX to Loctal, and found out NOS is not so smart.
  Production spread is huge, and some just arced on startup.
  I did manage to make a matched quad like that and a few pairs, but then what to do with them? 807s/6L6 are known for hideous amounts of 3rd harmonic distortion.
  The much vaunted KT66 was a distortion mush maker, but few seem to worry.
  
  As for the Bogen I will convert it to EBL71, another superb piece of kit with much lower distortion than any 6V6 and 2-3x the gain. Those also can be had for peanuts, as they made zillions of them in E Europe for lousy noisy old AM radio sets.
  They are supposed to run the same A-A load as the 6V6.
  Look how low the anode voltage can drop without losing linearity!
  It's going down to 20-40V and still conducting!
  
  Now compare it with the dirty old 6V6oids..
  
  Pentodes can reduce IMD, now you see why.
  That particular one (with the 2 redundant diodes) was scarcely ever imagined in push-pull and has no info on fixed bias at all.....ie. probably works brilliantly without all that beam tetrode IMD, and heavy THD.

Post a Followup:

FAQ

Post a Message!

Forgot Password?

Moniker (Username):
Password (Optional):
	Remember my Moniker & Password (What's this?) Eat Me
E-Mail (Optional):
Subject:

Message:	(Posts are subject to Content Rules)

Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:	Automagically notify you when someone responds.

To view your new posting or follow-up, click on the RELOAD or REFRESH button on your browser.

This post is made possible by the generous support of people like you and our sponsors: