I have a cheapie Shield TE 121 (Olson electronics)signal generator that is putting out RF but I can't get a tone for modulation. Fortunately it has an audio input and I can use an external audio source - but I would like it to function correctly. Anybody know anything about this model and likely places to look to correct this problem?

With some further info about the unit , maybe it can be figured out, particularly if a photo is supplied showing the total of the chassis bottom

components. In the interim, the tube line-up should initially help.
With no documentation of that product being available to me, BUT, being one of the
" MIGHTY OLSON " products I would be expecting the unit to be using a power transformer and its developed B+ and the
units filament supply . That being fed to a single triode tube for the RF oscillator function with a second triode filling in for the Audio
oscillator / modulator function. Some might use a dual purpose tube for that or possibly a triode -pentode.
At any rate one tube will be doing the RF work and the other providing the audio aspect. If that is an old unit you might initially inspect switch
contacts associated with switching in the AF mod function. And then if you look closely there might be a larger iron core transformer asociated
with being the combined reflex osc / modulation transformer.. Tracking down the wiring from that transformer going to a particular section of
a tube should confirm the tube associated with the AF osc circuitry. If the unit is in the internal modulation mode with the osc enghaged an.....
AC mode metering of the PLATE connection terminal of that tubes, should reveal a decent AC modulation level being prodiced. Flip the modulation off
to confirm its dropping off. If no AC signal is present, check for the basic B+ being present on that plate when the unit is in its internal mod mode.

Stoppping for Feed- Back time.....


73's de Edd

:I have a cheapie Shield TE 121 (Olson electronics)signal generator that is putting out RF but I can't get a tone for modulation. Fortunately it has an audio input and I can use an external audio source - but I would like it to function correctly. Anybody know anything about this model and likely places to look to correct this problem?

Edd, Here are some pics... the tube in the foreground is a 6AR5 and the tube elevated above it is a 12BH7-A.

Thanks...

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:With some further info about the unit , maybe it can be figured out, particularly if a photo is supplied showing the total of the chassis bottom
:
:components. In the interim, the tube line-up should initially help.
:With no documentation of that product being available to me, BUT, being one of the
: " MIGHTY OLSON " products I would be expecting the unit to be using a power transformer and its developed B+ and the
:units filament supply . That being fed to a single triode tube for the RF oscillator function with a second triode filling in for the Audio
:oscillator / modulator function. Some might use a dual purpose tube for that or possibly a triode -pentode.
:At any rate one tube will be doing the RF work and the other providing the audio aspect. If that is an old unit you might initially inspect switch
:contacts associated with switching in the AF mod function. And then if you look closely there might be a larger iron core transformer asociated
: with being the combined reflex osc / modulation transformer.. Tracking down the wiring from that transformer going to a particular section of
:a tube should confirm the tube associated with the AF osc circuitry. If the unit is in the internal modulation mode with the osc enghaged an.....
:AC mode metering of the PLATE connection terminal of that tubes, should reveal a decent AC modulation level being prodiced. Flip the modulation off
:to confirm its dropping off. If no AC signal is present, check for the basic B+ being present on that plate when the unit is in its internal mod mode.
:
:Stoppping for Feed- Back time.....
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:73's de Edd
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::I have a cheapie Shield TE 121 (Olson electronics)signal generator that is putting out RF but I can't get a tone for modulation. Fortunately it has an audio input and I can use an external audio source - but I would like it to function correctly. Anybody know anything about this model and likely places to look to correct this problem?

Edd, I narrowed it down to the circuitry around the 6AR5 - I pulled the tube and still got RF. I tested the tube again and it's good. I really not sure of the pin layout on this tube. Any more hints?

Heres the tube layout:
http://nj7p.org/Tube4.php?tube=6ar5

Thanks... Measuring plate to gnd I get around 40V with switch in ext mod that drops down to 30V on int. With my DVM - it gives weird reading on VAC but matches with my analog meter on VDC.

Sorry guys - my bad.... I pulled a few of the molded caps out of circuit and I get a fixed resistance on the 100K scale on 3 out of 3 - so I'll assume they are all bad and recap this thing.

Seven replaced caps later - I have audio modulation! These were cheesy-looking Japanese caps labelled "ZEUS" and EVERY SINGLE ONE was BAD. Looking at them under a magnifier, I see hairline cracks in the phenolic on most of them. Live and learn - forgive me for not doing my homework before posting.

Bill J, you might use EICO 324 RF Gen as a guide line. I believe you will find them very similar and possibly can create a schematic for your set by editting. PL

:Seven replaced caps later - I have audio modulation! These were cheesy-looking Japanese caps labelled "ZEUS" and EVERY SINGLE ONE was BAD. Looking at them under a magnifier, I see hairline cracks in the phenolic on most of them. Live and learn - forgive me for not doing my homework before posting.