Looking for circuit.
Valve line up, 6A7, 6F7, 6B7S, 42, 80.
Been given to me to repair.
Lots of daggy repair done over the years by the look of it.
Has three tuning gangs, and the circuits close to the line up and era don’t appear to have three nor the 6F7.
Has RF problems, and unfortunately critical valve sockets are mounted underneath the band switches, with components mounted obscuring the pins for measurements.
One I feel like handing back to the owner.
Can anyone help with an accurate circuit for this model.
JJ

Sets that I find with that line up:


Make, Year, Model, Chassis

Beale, 1937, 950W, , AC DW Console.
Kriesler, 1937, 710A, 710A, AC DW Console.
Kriesler, 1937, 711A, 710A, AC DW Console.
Kriesler, 1937, 712A, 710A, AC DW Console.
Kriesler, 1937, 720A, 710A, AC DW Console.

Thanks GTC.
Your right, but unfortunately no AORSM reference.
Hope someone might have something on the ones you mentioned.
JJ

I have physically seen one example where there were two Pentagrids. However, you may have to reverse engineer, before moving on?

Three gangs is odd and is more common where there is a pre amplifier unless two gangs are in parallel.

I have worked on American Midwest & some of them had four gangs, two being used for a Colpitts oscillator which none of the 700 ones presented have. That was also autodyne with separate exciter valve. There is no guarantee that the gang is original and a critical look at the chassis may be in order.

Photos may be helpful?

Most of those sets were designed to be assembled in layers, minimising construction time: Not any consideration for fixing. I did have a Stromberg Carlson where there are three caps under the RF switch box and it has to be substantially undone to get at them: Very time consuming.

This may be like the one Carl has where obvious signs of tampering should ring alarm bells and the circuit investigated & repaired before contemplating powering. I have had several sets that have come in suffering catastrophic damage & expensive damage, caused by the exuberance of plugging it in to see if it works.

I have two sets on the bench that were too unsafe to power. That also applies to battery sets, vibrator sets, & test equipment.

Marc

Thanks Marc,
I have done some reverse engineering/investigating and so far discovered.

The three gangs are in operation. RF pre amp 6F7, but interestingly the triode section appears to be the audio pre amp.

The mixer/oscillator 6A7 uses a tuned gang in its input and the last gang oscillator tuning.

The IF frequency I believe is supposed to be 252.5 Kcs, but at this stage can only get a very weak signal through at around 350Kcs.

I need to do some more looking and measuring, but everything I'm interested in is buried under band switches, large mica caps,
and coils.

I have audio with the generator but it is very weak and distorted. HT all good.
Think I may start with the audio section first while I think about how to attack the RF/IF section.
it could also be reflexed in the IF section.

Will report back when more of the wiring/caps and resistors have been checked and tidied up.
JJ

Kriesler model 701A: AORSM Volume 1 page 145

Should have purchased the CD, but have not got a suitable windows pc at present.
And it won't apparently work on Mac.
Have not got access to AORSM volume 1

Have not got access to AORSM volume 1

If you 'unhide' your email address, I'll send you that page.

P145 Vol 1 AORSM has models 700 and 710A. 710A has the appropriate lineup. Can provide a copy tomorrow if your email is unhidden.
The description on the page is:
Valves: 6A7 pentagrid converter; 6F7 twin section 1st and 2nd IF amplifier. 6B7S duo diode detector and AVC; 42 pentode audio output; IF 458KC

Thanks, guys. Much appreciated.
Email not hidden.
JJ

OK, sent. Hope it proves useful.

On its way.

Thanks GTC and Graham, what great technical friendship.
Have something to work on now.
Notice the 701A only uses two gangs, mine definitely uses three.
But it’s the right valve line up. Need to spend more time on it now that I have some more info.
Probably need a few days when time permits to get some result out of this unfamiliar chassis.
JJ

Westinghouse 556 an AC/DC set uses a three gang tuner.
Lineup is 6F7 RF amp and driver, 6A7 converter, 6B7 IF amp detector AVC, 43 audio amp, , 12Z3 rectifier.
Will send tomorrow if needed.

An interesting combination with 6F7 being a bit like the universal widget 6BL8; both being triode pentodes. Radiotron Handbook lists 6F7 in mixers & converters. You can use it as a mixer oscillator, or them individually in combination with another valve.

This being the path taken here. There is a note that due to large voltages from the 0scillator appearing on the signal grid circuit, That can reduce sensitivity on the SW band. IF is likely 252.5kHz; that sort of frequency I would set here with a counter. Ideal frequency for FAX machines and other Switch Mode PSU's & wall warts.