Trio 9r-59d repair hints

Hi, in a trio 9r-59d I experience a weird problem. On band B (1.6-4.8MHz) when I tune the dial below 2.5MHz or so, the receiver stops receiving anything, even noise. It seems to me that the local oscillator stops working at all below 2.5MHz on this band, cause even noise disappears.
It seems to me that when I set the band spread or main tuning capacitors to large values, oscillation ceases. In the schematic, this could be true, because these capacitors are connected in shunt to the feedback LC so they also "remove" signal from the feedback loop, apart from tuning.
What to check and how to fix the problem?

Manual and schematic here:http://www.iw2nmx.it/Kenwood%20-%20T...0Schematic.pdf

The most likely suspect by far is V3 losing efficiency. These are quite old receivers.
I have heard of users replacing V3a with a JFET, obviously with the supply dropped to a more reasonable voltage. It makes them far more stable as the original design was prone to drifting with voltage and temperature.

Brian.

Replacing ECC85 tube with a JFET is a good choice, but probably have to do a lot of re-tuning of the LC resonators after replacement.
Otherwise ECC85 was a very common tube in that period of time, and you can get from the net a brand new one at a decent price.

I have measured the voltage on the PSU diodes and it is around 210v, so ok. After R38, it is just above 180v which is again ok.
It is R39 that lowers down the voltage at 145v, which is too low according to the schematic.

I have also simulated the PSU (attached) and this verifies my findings.

But why R39 is shown as 1k? This is too much according to the above.

Simple Ohms Law would be enough!
From a DC perspective R38 and R39 are in series and as both are 1K they should drop the same voltage.
210v - 180v = 30v dropped across R38,
180v - 145v = 35v dropped across R39
So one or both has changed value. It is very unlikely that capacitor leakage is involved.

If I remember, one of the modifications to this receiver was to connect an OA2 regulator across R40 to regulate the VFO and BFO supply voltages, you could do the same with a 150V Zener diode these days.

Brian.

Mine has the regulator tube there. That is why I got around 150v, I just noticed that.

Hm... that is weird. It seems the problem has fixed by itself. After a few power on/off and a few switches changes, now the oscillator does oscillate.
That IS weird....