Here is a link on the 11-78. Has tips on finishing including the use of pumice powder as a filler, which is not available through the big supplier. He says stripping as a last resort as it can lead to changes in colour.

http://vintage-vibes.byethost16.com/index.php?p=1_11_Kriesler-Model-11-78&i=1

I have found that stripping removes the filler. An alternative that is supposed not to remove the filler is a cabinet maker's scraper. Haven't been game to try that given that you never know how much veneer is left, not mention damage if you slip.

I have been working with Veneer for many years and its quite tuff really. If you want to use a scraper its best to turn the edges down on a grinder.
The grain filler is what gives the finish contrast and the colour.
Before I restore any furniture I look at the grain and the finish with a magnifing glass and then I match the grain filler and the colour before I strip it.
Unfortunately in reality these finishes are 60 years old and whether there Nitro or Oil Varnish they will need to be stripped back and restored by now.

Has anyone ever manged to bust one open to see if it's copper corrosion, or something else?

Hi GTC,

I have unwound a couple and they are always mid way through the winding. No corrosion present but a black burn spot where the winding is open.

Most blown ones came from over used uncapped sets or chassis, but the common denominator also was the radiograms that were designed with lack of ventilation. They can be fully open or high resistance across windings. Strangely some still worked because of a capacitance effect I presume.

I have found replacing them with the Hammond units quite successful , but a good Kriesler O/P sounds better. Prefer donors as opposed to new. Once the power supply is restored I haven't had any fail in any of the chassis I have restored.

IFTs have had a green corrosion , but again came from sets that were over used and power supply caps stuffed. Other brands suffer the same fate also . HMV caprices N3 chassis have also got a high failure rate, more than Kriesler . Diode rectifiers and bad caps give that O/P a sudden 300 400 V jolt , and most have opened on shut down. They did have a factory upgrade because of bad O/Ps , but not many were replaced after sale from what I have seen. And every model with that brand O/P I have found dead. The failure was also progressive after the chassis was restored.

Vic

Thanks for that detailed reply, Vic.

Interesting to learn that burnouts are mostly responsible for the Kriesler OPT failures and your diagnosis make sense.

Also interesting to hear the HMV N3 story. It would be disheartening to have the OPT blow just after a resto, so good to know that's a high possibility if the OPT is original.

"Strangely some still worked because of a capacitance effect I presume"

Quite a few designs have negative feedback directly to the OP stage cathode.
When the transformer primary goes O/C, you are left with a cathode follower directly driving the speaker (and transformer secondary in parallel) using the screen grid as anode. Not nice, but you will get some sound until G2 melts down.

The main underlying cause of failure is paper insulation in the transformer. Paper has the same issues over time as it does in paper capacitors.

Have you ever seen a failed output transformer that used polyester wire and a plastic bobbin? I didn't think so!