need a little help with an HK solo2 tube receiver

[ke4mcl]

this old receiver started as a labor of love and has now become a personal challenge. i'm two steps away from gutting it for the iron but i'm stubborn and with every tube repair i learn something new.

its been recapped with all new coupling caps and lytics. i left the ceramics alone. the two 1k resistors in the pic get REALLY hot at 110v on the variac. the caps are new and do not get hot so i am assuming they are ok.

could the value on those have drifted down causing them to pass more current? the resistors are r27 and r28 in the schem.

[artosalo]

There are voltage readings (320 V and 292 V) given at both sides of R28/27.
If the readings are correct, then the power dissipated by both resistor is some 0,78 W/resistor. What are the existing voltages ?
Obviously at the left side the voltage is much less than 292 V. Since the schematic is not complete, it is difficult to say more.

[ke4mcl]

full schem here down loadable as a pdf about 3/4 way down the page
Harman Kardon - Product Support - TA12 (Solo II)

[DF96]

R27 and R28 are more likely to overheat if they rise in value, which is quite possible if they are carbon composition.

[ke4mcl]

sure enough they were both way off from each other and way over 1k. i replaced them and the new ones still get hot even at 100v on the variac. amp plays ok on aux and AM but fm is out.

i've heard that HK initally made lower end stuff. this receiver uses a pc board in 1957. the iron is of decent size and the tubes are well chosen but the rest leaves much to be desired. i wonder if the rest of the carbon comps are shot as well?

i put the covers back on and put it on the shelf for now. i'm almost about to give up on this one and just break it down for parts.

[DF96]

You are likely to find that many, although not all, of the carbon comp resistors have changed value. Don't worry too much about small changes - in most cases 20% does little harm.

[artosalo]

sure enough they were both way off from each other and way over 1k. i replaced them and the new ones still get hot even at 100v on the variac.

Can't you simply measure the voltages at both end of R27 and R28 ???
If the voltage drop is too high, then excessive current goes somewhere. This kind of fault must be located by measuring.

I can not find the schematic. The link you gave goes the HK country selector page only.

[rmyauck]

I found it under Canada, support, all products, and it's too big to upload.

[ke4mcl]

while i can get in there to measure, those resistors are notoriously close to the bare power switch leads. to add to the annoyance all the wire is brittle. in order to fit the new resistors in i had to stick a shim of fish paper in. the leads on the power switch are that close. a little face flex and it would be a sparking good time!

i'm a collector at heart but at the end of the day if i get it going right its an unremarkeable mono receiver. i'm setting it aside for now in the "trade it off or strip it down pile". the tubes and iron alone in this unit would make a real nice setup for a great mono amp or guitar amp. other projects await.

thanks all