[Phlogiston]

Now I need another Scott 510 Power supply/amp for stereo.

https://www.russoldradios.com/blog

   

[Phlogiston]

I also just completed a small stereo pre-amp. It uses 2 12AT7s which may be replaced with two 12AX7s for more gain. One triode drives the second, but a switch allows the injection of a signal at the grid of the 2nd triode if less gain is needed.

It has its own PS with B+ at 180V and the filaments running in parallel at 6.3V. It measures 7 1/2 x 3 x 3" including the veneered wooden cabinet. I tested it with a HK audio generator (a very cool device in it's own right) and it can pass signals from 1hz (no gain - probably some loss) up to 50,000Hz (and beyond). It is +/- 3db between 20hz to better than 20khz depending somewhat on input level and the gain adjustment which is a 650K stereo pot between the triode sections ( wanted a 1M pot but didn't have one). Two sets of RCA in (one high level, one low) and stereo RCA out.

It can also be used as a mixer for stereo into mono.


P.S. If not using the 1st triode - ground the input. No sense in having it sitting there howling, even if you can't hear it.

I have added both of these devices to my work bench. Now I won't have to go dig up an amp when needed to test a project. It has already paid off in testing a Fisher receiver last evening.

   

[Phlogiston]

NOTE (!):

Testing down to 1hz can be rough on speakers.

Upgrade woofer in test speaker to 15W from 4W.

P.S. Just "popped" the old one apart - with a hammer. It did not burn out the VC, just ripped it off of the former. Cool!

[Ron Ramirez]

So was that built on an old Scott chassis?

Neat Fisher Series 80. I have its little brother, an AM (only) tuner that I picked up at Kutztown back in May of this year.

[Phlogiston]

It is a Scott 510 PS/Amp - rercapped and rewired to use the unneeded choke and rectifier socket. The choke makes the PS quiet enough for 3 stages of amplification and the unused socket became the preamp/mixer 6SL7.

Also, keep in mind that none of the modifications are permanent. If one day somebody needs a real 510 amp, a few wiring changes will return it to original.

I'm using it to work on a Meissner 9-1091C right now (the Meissner has no amp on the RF chassis).

[Phlogiston]

P.S.

Beating on the Meissner now for the last 4 hrs trying to figure out why the FM RX level kept changing - like a drum beat - up down up down. The RSSI (eye tube) also changed.

It was the 6BE6, RF amp for AM. The filament warmed up - then opened, cooled and lit again - repeat. You would not think it would have made such a difference on the separate FM path. No wonder I can't get anything done.

In testing I see that the emissions from the tube were on - off - on faster than would be expected because of thermal inertia. So there might have been another internal intermittent, yet the result was the same and was resolved with replacement.

Two more Meissners to go. Moving on to the two 9-1093s.

[BrendaAnnD]

Never seen a 6BE6 as an AM RF amp. Those are usually heptodes like 6BA6/6AU6/6BJ6. 6BE6 is a pentagrid converter, used as oscillator/1st detector stage for AM. I've seen them used for FM as well. Not all that good at it, but they do work with clever engineering.

[Phlogiston]

Never seen a 6BE6 as an AM RF amp. Those are usually heptodes like 6BA6/6AU6/6BJ6. 6BE6 is a pentagrid converter, used as oscillator/1st detector stage for AM. I've seen them used for FM as well. Not all that good at it, but they do work with clever engineering.

Yes - exactly. The converter tube for AM was powering up -down. The voltage change this was causing (mostly a small change in fil voltage) was messing up my FM sweep(s).