Reginald

After many years of operation, my wife's much loved Kriesler 11:60 mantle radio has 'given up the ghost' and I need to fix it.

The audio cannot be turned down on a strong station. Tracing the wiring it seems to have an unusual AGC circuit.

Would any one have a copy of the schematic for this radio that they can send me?

Thanks
Reg
(reginaldgauci.org)

Roboz6

Reg,

Just checking that you have the two control model with valve lineup of 6AN7, 6N8, 6M5, 6V4. If so, I have a copy of the circuit in pdf format which is reasonably legibil. Send me a personal email (rob.wilcox1bigpond.com) and I will send it to you.

Regards

Rob

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Rob

Marcc

If its got paper caps in it, get rid of those, whilst you await the circuit.

Have a look at the pots despite that being a strange arrangement. In a normal setup I would expect a high resistance on the earth side of the volume pot. and that would include resistors going open or high.

Something like that may have happened here despite there being two controls. I would scratch around the second control first.

Marc

Marcc

That's assuming its a two pot model like 11-59

Reginald

Thanks Marcc.

Only one cap was still paper and it was leaking. Still one would expect it to be crook after 50 years or so. Most of the resistors were changed when I purchased the radio some two years back. Volume pot is a single and checks OK.

I think that the AGC coupled with the reflex design of the 11:60 circuit can't handle the main ABC station (6WF) as it is only a few kilometres away. Sadly, this is the station that my wife always tunes to.

As a work around, I have shortned the wire aerial to abnout 30cm and the performance is acceptable.

Regards
Reg

Marcc

Overloading the front end is possible, although I tend to not have too much trouble with a Philips 132L and a Little NIpper (1957), with 66 ft of antenna & 2RN only 8Km away & 3NE not much further. I can see the towers, there isn't much in their path.

I would (just in case) check the resistance of the AGC resisors and make sure that the earth side of the pot has no dry joints as it looks like the pot itself maybe OK.

When you get the circuit do ahead count & make sure that caps are those specified. In that sort of set their value is critical.

Marc

Reginald

Hello Marcc. Thanks for the suggestions.

The two 1Mohm AGC resistors are new 5% ones and are OK. There is no earth side to the pot as it goes to a series 150 ohm resistor to ground and a 390ohm resistor to the secondary of the speaker transformer.

The centre arm of the pot feeds the audio signal back through the IF amplifier (6N8) and it is used to 'bump up' the audio signal. The audio signal is then picked up by the grid of the audio output valve (6M5) from the anode of the 6N8 via the primary of the final IF transformer and the RF component is bypassed to ground by a 1000pF capacitor.

The AC component of the audio signal on the centre wiper of the pot is fed back via an isolation capacitor and a 1 Mohm resistor to the earthy side of the aerial coil. A second 1 Mohm is also attached to the earthy side of the aerial coil and the resistor picks up the audio and bypassed DC component of the audio signal directly from the of the secondary side the final IF transformer which (via a 47K resistor) also feeds the top of the pot.

This rudementary AGC circuit copes fine with most normal level radio stations but can't seem to cope with the ABC's high signal strength. Even with the pot wound to minimum, the audio can still be heard.

I have never seen any other commercial set 'reflexing' the audio (back) through the IF amplifier. I guess that they built these radios to a price to suit their intended market.

Reducing the aerial lenght seems to 'fix' the problem as she never changes the station.

Reg

PS The schematic was kindly sent by Roboz6. If you want a copy let me know.

Marcc

Just for info:

Got serious with a HMV 62/52 today after the new pots turned up. Similar behavior to 11/60 , only obvious distortion & fairly deaf.

Volume pot was just plain worn out and so bad that it was not worth the effort to try & fix the set with it in there. Tone was 870K (grid leak) should be 500k. Cause of main problem, 10pF SM on the plate of 6BA6 (RF amp) feeding DC into the AGC (tested 12.5M 500VDC).

Marc

Reginald

The leaky 10Pf problem is interesting as I have not checked any of the mica or ceramic caps at high voltages as I don't have a suitable tester. I think there was a project in Silicon Chip for a cap tester a few months ago. I will go through my back issues and check it out.

Ta - Reg

Marcc

It is rare for SM's in Australian sets to fail, however.... knowing that... it is the wisdom of fools, to preclude them when fault finding. I have one of these sets of my own.

It must have been a bad batch of everything as I ended up replacing every resistor & capacitor in it.

The most likely SM's to let go, are any with high voltage DC on them. The 10pF being on a plate, was a standout, for "a most likely to fail".

The best method for testing the leakage of non polarised HV caps, in a valve radio, is to test them (one end out of circuit) as close to their rated voltage as is possible.

Some of the old "Valve & Circiut Testers" had crude but effective circuits for testing the valve radio caps.

I would compare what equipment you have, to what cost is involved in adding the function you need, and your confidence in building kits.

Because I can do Tag & Test , I actually found it expedient to by a Q1242 Insulation Tester from Altronics, rather than build one, as it had the voltages appropriate to my needs.

Marc

Reginald

The SC Capacitance Leakage Meter only goes to 100V. The Kriesler has voltages to over 200V around the Audio Output Stage with some at over 90volts around the RF/IF/OSC sections.

The Q1242 sells for around $120. For my needs, it is probably a bit too expensive.

I might just lift off one end of the caps that are across a high voltage and check with a voltmeter to ground.

Reg

Marcc

That does not sound like a particularly reliable method. You really need to be able to measure the current through the cap.

The VCT valve tester I have actually uses a neon for an indicator. These devices need not be complex, but you really cannot test caps in a radio without an external source of HT.

Basically the megger is an ohmeter with a bigger bittier power supply.

You can make a current limited, switched voltage source, with an LR8 it will take 450VDC in.

I note the issue with the SC leakage tester. VCT was built in 1938. and is around 225V on the cap tester. This is current limited & can reform electrolytics if they are not too far gone, or have been stored for over 2 years.

Kriesler is only a baby with some of those volts. A "Lyric" I repaired has 375 VDC on the output valve plate (50). An amp I have has 310 VDC on the plates of the 6CM5's. Highest valve voltage I have seen, but not worked on was30KV.

Marc

2MuchJunk

I have just found a circuit for a Kriesler 11-90 in a vintage radio article in Silicon Chip magazine (June 04), with a valve line up of 6AN7, 6N8, 6GV8, and 6V4.
I would be happy to scan the circuit and email it if you think it may help.
I'm not familiar with either set, and don't know what similarities there may be.

Marcc

Looking at the correct circuit, may lead to less speculation. Beware with new resistors, I have noticed a few supermarket ones of late that have bad colours ( I trained as a dyer & pilot ..... no colour issues) and unbelieveably were out of spec.

Reflexed valves are running AVC, RF, Audio and are also detecting.
So the feedback from the speaker tends to go their.

If there is a new 150 Ohm resistor on the pot , check to see that it is in fact that, and not 1K5.

Marc