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Joel 12th June 2003 05:50 PM

A 10W ultralinear amplifier with unique features.
2 Attachment(s)
Nuvistor front end, transformer phase inverter, and gas-tube regulation/filtering. It all fits in a 6"x10"x2" chassis too.

Constructive comments are welcome.



fragman56 12th June 2003 06:15 PM

Good to see some more of your designs. I like the 6aq5. Only heard them through a Hammond 125ese, though. Very strong!

Pictures coming?

How about your tiny, DHT P-P with trafo inversion? How did that turn out?


Joel 12th June 2003 06:19 PM

Hi Rick,
The Lundahl transformer just arrived yesterday, so I'll be drilling the chassis this weekend. I have all the parts gathered except the 0B2 tube. I will post picks as soon as it's done.

The 30/31 push-pull is still in the dream stages.

This one I came up with because I wanted a 10 watt tube amp to do a direct comparison with my 10 watt SS amp.

dhaen 12th June 2003 06:34 PM


JLH 10W?

Joel 12th June 2003 06:44 PM

Yes, it's the JLH, strictly 1969 version. I didn't even add Linsley-Hood's 1970 updates, since he said his units were unmodified. Nice sounding amp.

dhaen 12th June 2003 06:50 PM


For once (of late) I agree with you. I built it in 69-70 in original form. Later I scaled it to 50W. The heatsink was 2 foot square and needed forced air cooling! Parties could be heard at the end of the street. Police were called on occasions - but that was in my youth.

Back to the sound: Very similar to a reasonable P-P valve amp. beats any mediocre valve amp.


Joel 12th June 2003 07:06 PM

Well, we'll see - I have high expectations for this 6AQ5 amp. Whereas with the JLH I had none.

qwad 12th June 2003 07:21 PM

AAAAH THE 6AQ5, :D by all accounts a much under rated and neglected tube, with great potential one of joe, [forget his last name ]a frequent poster on audio assylum tubes forum, he reckons it will out perform any of the el-84's for sound quality:rolleyes: , and cheap to find even in nos on ebay as it hasn't developed a "cult"following like some other tubes, from what I understand it can even be used to replace the 6bq5 in a circuit as it has many characteristics the same, there was a low power circuit from dynaco I had one time that could use either the 6bq5or 6aq5 without any major mods, good choice for a simple amp I LIKE THE circuit:nod: :drink:cheers, TC

EC8010 12th June 2003 08:29 PM

A couple of thoughts.

With a shared cathode resistor, your output transformer will almost certainly have an out-of-balance DC - unless you match the valves.

At power-up, when the 6AQ5s are cold, those neon regulators will have to sink a lot of current. Are they up to it?

James D. 12th June 2003 09:01 PM

Joel's back with a vengance...
Hi Joel,

Great design, interesting tubes and an individual take on topology. That's what we have been missing!:nod:

Constructive comments... let me see.... what would I try...

1) Snubbing the 1N4007s does clean up the reverse shutoff switch and might help the sound

2) split the 5.5k resisitor feeding the OB3 for a choke (156C say) cap into resistor might add to the dynamics a bit - but probably wouldn't as this seems to work better with pp.

3) Fixed battery bias???

4)try a 1uF capacitor between the OPT B+ feed and the cathode junction of the 6AQ5s - about all the gas regs would allow?

but I like it as it is. Nice, really nice.



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