Hi everyone!

I occasionally feel the need to tinker with my old stereogram....as I'm sure we all do!

I previously build a rod elliot P06 phono preamp to run a magnetic cartridge on the turntable...rewiring the tonearm & routing to the new independently powered (torroidal transformer) preamp.

I then fed this output to the grid of the 12AX7 Kriesler preamp via 2 x 1μF coupling caps.

Now I think this is a "new" fault but when the volume is turned to NIL, there is still sound from the right channel!

No matter what I change at the rod elliot pre amp, the right channel is the only one with this issue so it doesn't seem to be the preamp.

It isn't the case when on radio, only phono where some of the signal is bleeding through to the output.

I was wondering whether there could possibly somehow be an issue with the rca ground of each channel where it connected to the chassis at 12AX7? For curiosity sake put a coupling cap on the channel grounds incase there was any dc on the ground for whatever reason but this made no difference. Is it ever normal to put coupling caps on the channel grounds or is that just silly?

Has anyone else connected a phono preamp to a tube stereogram? The other thing I could try is feeding the Rod elliot phono preamp directly to the volume input...although that removes the Kriesler pre amp which wasn't my preference and I'm sure this problem was not there only a couple of months ago.

Does anyone have any ideas? I can't see any visible bridging on the chassis and I swapped out the 12AX7 just incase there was some internal issue...I measured volume pot resistance and both channels are the same. Any ideas on how the signal is leaking through to the output stage??

Just to provide a quick update - I have had no progress in finding the above fault but I have discovered a new one.....one of the primaries on the RH output channel is cooked! It was just operating off 1/2 from V4 side....with nothing from V5 working.

So have two queries now - 1. can this somehow cause the bleedthrough when volume is off? 2. Where do I start looking for a replacement push pull transformer....there are some single ended available at Jaycar but I can't find push pull outputs.

It seems Hammond make some:

https://www.tubesandmore.com/products/transformer-hammond-universal-push-pull
https://www.radiodaze.com/universal-push-pull-tube-output/

Would this be the way to go or does anyone know of any more easily obtainable options?

The schematic shows I require 10k CT 15 ohm - which I think means 10k primary impedance centretapped on primary and 15 speaker impedence? The DCR seems to be 700 ohm but the Hammond are all 285 ohm....will this burn out the 6gw8's / can I just add a resistor on each end of the primary?


Thanks for any help.

one of the primaries on the RH output channel is cooked!

A well known problem with Krielser is OP transformer failure.

My Kriesler console blew its push-pull transformer with its previous owner, and the repairer replaced it with a power transformer.

After I purchased it, I found that it had been connected incorrectly, and that bare wires were arcing to the chassis, so I had to fix all that. After that it worked well, and still does.

If you have a spare power transformer, connect the centre-tapped side to the output valves, with the centre-tap being the HT supply. The speaker is connected to the 6.3 volt winding. The original mains input winding is not used.

Yep GTC spot on!

Just trying to find a work around now….i replaced all the caps before I even plugged it in but guess it still happens - I do listen to it loud sometimes 😂

That’s interesting Rob…do you notice a different sound from RH to LH or does the power trans work just the same?

My Kriesler is a mono model, so I can't really answer the question.

Hi guys,

Well a few updates - I have managed to grab hold of a spare chassis of the same model in order to see if this solves both problems.

These output transformers tested well with no open primaries & upon recapping it and firing it up it sounds a lot better! (although I did up the cathode bypass caps a little from 25μF to 27μF which may have helped with a bit extra bass).

Now upon connecting up the preamp.....same issue! WIth volume turned off you can still hear it play through the right channel!

I have double checked with the multimeter all of the headshell wiring and pins....they are all going to the right place....so I don't have any idea what the issue is other than it must be a design issue? I have tinkered with the grounds a bit but nothing seems to make any difference. I have added 1μF coupling caps on the 2 signal positives and the signal ground too (they merge at the turntable so I added it there) so it's all decoupled for dc purposes.

In any event it works well enough and sounds good for now!

One of the things to study is how it is wired, when there is a switch to silence the RF section. Some cut off a screen, others the signal path.

In cases of design amnesia, check that they have not made the boo boo and left the AGC connected? That will behave like a dead oscillator or IF with a weak signal from a strong station, getting into the detector first audio, via the AGC (where fitted). In rare cases RF can ride on B+ and chokes and / or better decoupling caps are fitted to shut it up,

I have, in some cases, followed what they did with infinite impedance detectors and put RF chokes on some tubes to stop them amplifying RF. Some tubes are not particularly fussy about what they amplify, and that can be a problem.

I have found with early Kriesler radios, of 10, two might have a good output transformer. Its an attrition rate with them.

Thanks Marcc you've helped me on countless other radios!

The bleedthrough is still the vinyl playing when the volume is turned to zero...so doesn't seem to be in the rf section.....but definitely only the RH channel not LH.

If I connect the phono preamp to the old phono input cable then it runs through a resistor/cap combo before being fed to the 12AX7 which quietens it a bit.....but doesn't sound as good. Running the phono preamp directly to the valve grid (bypassing the resistor/cap) makes it louder such that you can still hear the high RH channel at low volumes.

I could try running it to the volume switch input instead?

Do you have any idea why the outputs trans fail so frequently on the Krieslers? When there is no alternative do you recommend going for the Hammonds 10w? Apparently sound a lot better have you tried it before on any?

The reason the Kriesler transformers fail is down to the wax impregnation, which over time allows moisture ingress (both wax and paper are hygroscopic) and corrosion.

It would make sense to take any existing ones and do the Prepsol soak, followed by turps, followed by a long soak in clear polyester marine lacquer, as we have done with considerable success with TV horizontal output transformers.

I have acquired a lot of scrap radios and output transformers and have used line transformers, so I have not had to buy transformers.

CRC do make a mar suitable for windings "Urethane Seal Coat" and I have used that on coils etc.

What one has to be really careful of with magnetic cartridges is wiping out the bias of the tube, or transistor. In some cases if the radio its being coupled to, that also includes back bias being shorted out. That is likely why there may need to DC blocking of the ground as well as the feed line.

On that I have noted a Philips of the late forty's with a magnetic pickup that floated and had a matching circuit before the tube: It is back biased. There is, by changing the circuit, a risk of the tube getting too much input and distorting.

I would be looking at how the turntable is disconnected before speculating, but there is possibly a leakage path, or dodgy ground. Ideally the turntable chassis and radio, or amp chassis should be at the same potential difference (0), to prevent ground loops. Often manifesting as hum.

Ah thanks Ian & Marcc, interesting I didnt'know they can be recoated like that....do you just unsolder them and dip them?
Or do they have to be disassembled? I have an old parts chassis from a 11-95 kicking around...might try pulling one apart just to learn about them.

WIth the working ones in my Kriesler 11-97 I guess it becomes a case of whether I try to keep them working or just splurge on a hammond replacement when the time comes - some say they sound better anyway so I wonder.....

Ah thanks Ian & Marcc, interesting I didnt know they can be recoated like that....do you just unsolder them and dip them?
Or do they have to be disassembled? I have an old parts chassis from a 11-95 kicking around...might try pulling one apart just to learn about them.

With the working ones in my Kriesler 11-97 I guess it becomes a case of whether I try to keep them working or just splurge on a hammond replacement when the time comes - some say they sound better anyway so I wonder.....

With the phono preamp I still get the vinyl volume coming through at zero volume so it must just be a design issue.
I have 1UF cap on both positive signal wires and the combined signal grounds before they connect to the chassis.

The turntable chassis ground is grounded to the preamp and chassis....I guess that's a risk of this setup...the chassis of the 11-97 should be zero but I guess there's a risk the preamp ground is not zero....if I disconnect the preamp from the ground wire and then use my multimeter to check voltage with one pointer on the phono ground wire and the other on the 11-97 chassis that would tell me wouldn't it? Perhaps that is what I should do.

Other than all that it sounds really really good now with a new cartridge I installed the Autotechnica DJ elliptical cart which tracks at 4g for a bit more hifi than the old Ortofon DJ conical and the latter definitely is better for home listening. With the limitations of the old at6 changer though I think I'll start looking for a later model turntable that I can fit in the same footprint....apparently the at60 tracks lighter due to to the auto trip slide low friction insert....so may start keeping an eye out for one to put in my console.

Just coating them will not work, all that does is seal the moisture in.

You don't have to disassemble the transformer.

My fellow restorer Pete uses Prepsol - a day's soak removes all the wax, which is hygroscopic.

He follows that up with a day soaking in Turps, which is compatible with the polyester lacquer..

After that, another day soaking in oil-based marine grade clear polyester lacquer. Make sure you get the type that cleans up with turps, NO water-based stuff here!

Let that dry for a few days and you will be rewarded with a transformer that will last forever!

The idea is to replace all the wax with polyester.

When we are treating a TV horizontal output transformer, where the EHT winding develops around 20,000 volts, we apply several coats of polyester to build up protection against corona.

There have been a few occasions here where various transformers have actually, been in a flood. Naturally they were saturated with water. The success rate was very high when put in a fan forced oven at around 50 degrees, which is actually the temp used to sterilise harvesters moving through vineyards.

This could be a way of driving out water & low temp wax? I have placed antenna coils on absorbent paper an soaked the wax off to repair an outside break and after that sealed it with "Urethane Seal Coat" which is for motor & generator windings.