rogerstube: Low Voltage

I still haven't solved the trouble with this Rogers Majestic 15/51 The DC voltages seem to be all low especially for the 12Q7 tube...32v..However, I do get a loud hum when placing my finger on the grid cap of this tube and when placing a screwdriver on the gridcap,  with my finger on the screwdriver I pick up a station although very weak......Any ideas as to what may be wrong with this radio?? I have replaced just about all of the capacitors including a resistor which ran from pin 5 of 35L6 to pin 3 of 12Q7.

Thanks

Job

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Hi Job,

                    Do you have a Circuit Diagram (Schematic) for the Rogers Majestic 15/51?   This would be of great use to all of us if you have.  I am sure that with that the brainpower of electronics, on the Radiomuseum.org, would be able and most willing to help you then.  Without, it becomes rather difficult.

Regards John C.

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Hello Mr. Goudie.

 

I see, none can assist you.

My english is not so good, but in Radio-Technic i am firm and i think whe find a solution for jour Problem.

 

First,  i think the low voltage on plate 12SQ7 is not the reason why that radio dont works.

Can you show here what Voltmeter you are using. Important to read the right voltage on Plate 12SQ7 is the input-resistance from Voltmeter, e.g. 10.000 Ohm / Volts or something.

 

If in the circuit a high resistance, the inputresistance is verry important.

I think also, this voltage is enough to bring reception. Your finger an top of 12SQ7 is a Audion -effect, you hear a station not via RF-Stage of your set.

 

Can you say here, what is your problem exept the lower voltage?. What is your observe?

 

Regrads Hans

here the right and good circuit from Mr. Birkner:

 www.radiomuseum.org/protect-path.cfm

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Good Day Hans--------Thank you for expressing an interest in this radio. First, let me say that I replaced the resistor which runs from pin 3 of 12Q7 to pin 4 of 35L6. This increased the plate voltage of 12Q7 to 48v. Although, all of the tube voltages are still low, like you I belive they are high ebough to receive reception.

Now my ignorance comes to the forefront.......My multimeter is a digital, Mastercraft brand and I'm assuming it is adequate for my needs.....sorry, but I don't know what else to say. The radio gives a low hum but don't respond at all to the portable loop antenna which I'm using.....no indication of a radio station.  Could it be one of the transformers???

Regards.......Job

 

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Hello Job,

now herer  the advises . Enclosed you find two sketsches.

Local-Oscillator and IF-Part_ testing.

the "rogers"  can have two failures, 1. local-oscillator dont works and 2.  the IF-Parts,  Filters and Tubes  12A8 and 12SK7 do not works,  or not correct.

The arangments of me,  will help to find out what is wrong?    

On the IF-test, the first Radio is tuned to a Radio-Station, with the coupling from Diode to the Antenna- Tunning-Condenser  C1 the "rogers" receives the IF =455 kc (with programm)  from Radio 1.

I recommend, to make the local-osc_test at first, i very easier to make.

NEW:

Be Carefull ! Between the two sets electical Shock is given ,  if they have not a Transformer in the Power-Line

If you can not understand what i mean, give me a mail.

Later whe can here shows our results.

I wish you a good proceeding.

regards  HANS  

Attachments:

• Local-Osc._test (16 KB)
• IF-Part-function_testing (24 KB)
• Mixer with local-oscillator (55 KB)

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Hans------Thanks for the suggested testing. I will procede with those suggestions tomorrow and report back.

Regards

Job

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Hans-----I have done the tests as per your instructions and I'll now tell you the results. First, I connected a 220k resistor to the positive lead (tip) of my multitester and connected it to pin 5 of 12A8M......maybe this was wrong?.... Then I connected the negative tip of my multitester to ground. My results were minus .33V....If what I done was right I'm assuming something is drastically wrong.

As for the IF testing, I did connecting the second radio to the antenna lead-in of Rogers 15/51 but I did not receive a signal. I"m not sure if I did everything correct or not and the snallest cappacitor was .005uf, so I don't know if that would be the reason for no reception or not.

However, although I have not received reception on this radio I am learning new things and that is what is important to me.

Thanks ever so much.

Job

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I just want to let everyone know that I have not given up on this radio. Hans has given me valuable advise and I have followed his instructions to the best of my abilities...it is possible that I did someting wrong. However, we did not find out anything which would solve our problems. I now have a signal generator on the way from ebay and I'm hoping that this will help me. Hans, I will let you know when the signal generator arrives and we'll continue to bring this radio back to life.

Regards everyone.

Job

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