'6AR5 -> 6AQ5 substitution'
Author:Kenny Martens (guest: search)
Date: Thu, Mar 24th, 2005 @ 15:20 ( . )

Hello,

I recently aquired a 10W old Jennen amp that uses a pair of push pull 6AR5's in the output and I've got some NOS 6005 (=6AQ5) tubes I would want to use in it. The pinout is ok, and i checked it out, they pull a lot more current, but the PT doesn't seem to get too hot.
Now here's the problem, I've checked the 6.3VAC at the pilot light while playing and it drops to a little over 6.2 while playing hard (the lowest it goes with the 6AR5's is 6.33V)
I know the heaters for the 2 6005 consume about 100ma more than the 6AR5.
I don't think it's really a problem since nothing except the power tubes gets really hot, and the fuse isn't blowing, but if any of you know why it wouldn't be a good thing if the 6.3 sinks so much lower, please tell me :)

Greetings and thanks again for all this goodness,

Kenny

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'6AR5 -> 6AQ5 substitution'
Author:stringbend (guest: search)
Date: Thu, Mar 24th, 2005 @ 16:06 ( . )

Hi Kenny:
On the one hand, clearly your PT is being taxed more with the substitute tubes. On the other hand, as you suggest... it seems unlikely to be a major concern. Monitor the heat of your PT after long-term use and use your best judgment from there. A small 6.3 tranny could be installed to handle only the preamp or poweramp but *probably* isn't necessary.

BTW...
I've never monitored the filaments under use.
Nor have I ever heard it recommended. I'd use the idle data instead.
I would suggest comparing the filaments at idle (but warmed-up) with both power tubes. Sounds like you'll see very little drop and little reason for concern.

BTW...
I have found that tubes are a little less noisey when run closer to 6V rather than 6.3 (or higher).
I prefer to run slightly below 6V... tube life is shortened - in theory - but I've never seen a noticable difference or had any problems in this regard.

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'6AR5 -> 6AQ5 substitution'
Author:Kenny (guest: search)
Date: Thu, Mar 24th, 2005 @ 16:12 ( . )

Good to know,

By the way I've monitored them a little longer and they generally drift back to 6.33, maybe it was just a fluctuation on the powerline...

Anyway everything seems to be coping just fine ;)

Thanks for the input,
K

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'6AR5 -> 6AQ5 substitution'
Author:Sean Weatherford (guest: search)
Date: Thu, Mar 24th, 2005 @ 19:02 ( . )

I would worry about the OT also, the 6AQ5's will give about 5 more Audio watts than the 6AR5's. The 6AR5 has the same performance as the 6K6.

What amp is it? The only amp I have ever seen with 6AR5's was some of teh old Western Auto Trutone amps. A pair of 6AV6's, a single 12AU7 and the 6AR5's.

Sean Weatherford
BEan's Amp Repair
Central, SC

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'6AR5 -> 6AQ5 substitution'
Author:Brendan (guest: search)
Date: Thu, Mar 24th, 2005 @ 19:06 ( . )

Tubes have a +/-10% tolerance.

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'6AR5 -> 6AQ5 substitution'
Author:Kenny (guest: search)
Date: Fri, Mar 25th, 2005 @ 00:43 ( . )

It's an old Jennen amp, i think it's from holland (I'm in Belgium by the way)
It's wired point to point with overspec'd wirewound resistors, i think everything's pretty overrated for the job,and the OT barely even gets any hotter while playing, the PT gets a little warm, but it's a very long way from burning your finger...
By the way the tube lineup is 4 6AV6's (1 tremolo, 1 input stage, 2 long tail pair) 2 6AR6's and 1 6X4.
The only thing that seems overly taxed with the 6AQ5's is the rectifier, but at idle it's still under the limit for the 6X4, at max signal it's about 10ma over the max, but i figure that'll just give me some more sag, so no real problems there, no sag till about 7-8 on the dial, ideal ;)
The 6AQ5's are only biased at about 55% of max dissipation and the screens are at 180 while the plates are at 250, so I think it's pretty well all under control ;)
It sounds awesome pushed by a boss hyperfuzz set for clean boost ;) huge volume out of a little open backed suitcase with 2 8" alnico's.

Sorry to ramble on but I'm pretty excited about it, thanks for the input, I'm sleeping on both ears ;)

K

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