Yes I see what you did there, I was never going to learn to type it

Monaro, I think there is a reason it's bad to parallel connect capacitors in order to achieve the sum of both values.
There are online calculators that let you get real tricky with making resistors in a similar fashion,
but someone else might advise about doing this with caps.

I did some research before I recapped it and read that it is fine to add capacitance in parallel (can also add voltage in series but not recommended because the first cap receives a higher voltage and can burn out).

However i'm an amateur and definitely stand to be corrected!

Just about to solder in the .0022 and .0047 caps in both my Krieslers now so will see how I go!

Ok folks!!!

Attacked the 11-77 first and replaced the two .0022 caps and the .0047 cap and fired her up!

And crackle!!!!!!!!!

So after a bit of cursing and a beer I replaced the two 100pf micas attached to the 12ax7 valve.

FIXED!!!!!!!!!!!!!!!

No crackle and beautiful sound! The forum's help has resurrected another old valve radio!

Oh no you won't believe it......

swapped the caps on the 11-97 and now I have a soft left channel

It could have been like that prior i'm not 100% but it definitely has no left and swapping the RH & LH pair of valves does nothing.

I replaced the .0047 caps again (I ordered 2 spares) just incase one was faulty and no difference.

I have gone over every possible connection nearby and cannot find anything that looks to be a problem.

I don't want to jump the gun and think it's an output trans but how would I know if it was?

Fixed one, lost another gotta love antiques!

That's no good

Easy way to test the output tranny would be to swap their
primary connections which would also swap left & right channels, but if something did fry a coil it might not be good to risk the other one.

You can disconnect them completely, primary and secondary,
and a multimeter will show some resistance across both primary and secondary,
if there is no resistance at all that's an open coil,
but you can compare one unit to the other as well because you have the pair.


Anyone can make simple mistakes, one way to check is
print a schematic and use a hilighter to trace every component connection on the printout as you check it against the real circuit, maybe just the area you worked on.

Thanks Art, hmmm maybe i'll just swap them and see.

I really was careful replacing the caps and I have started at every connection nearby for ages now and cannot see any connections bridged or errant.

I cut the old caps so the strands were left and I was easily able to see where the old cap was and I can see I have put them in the right place.

Since Krieslers seem to churn through the output trans I guess its somewhat likely it just died........I could have used it too long with the old .0047 caps in it or maybe the sub connection interfered I don't know.

I have just examined it a bit further and notice that if the treble is turned right up the left channel comes back probably about half of the power of the right but turned to the bass the left is really weak.

So seems its mainly the bass that is lacking in the left channel.

I think bass takes much more power to produce? So that could point to weak output trans although i'm sure i've read they usually either work or don't!

The more I think of it I did usually turn the balance to the left a little bit to equalise them but now its heaps more and still lacking bass!

I think i'll look at it tomorrow and try swapping the primary output trans and see what happens but for tonight i'm off to bed!

As said before, crackle is the realm of Silver Mica's and sometimes Styroseals.

If it was working before you touched it and is still making noise,it more likely you & not the transformer. Check as to what fell off,or where you should have put the cap.

Make sure a blob of solder did not short something.

I was never going to learn to type it...

You can find other units of measurement and special characters by going to Start - Run and typing charmap. The dialogue box shows all the available characters in the font you are using at the time.

Sorry I think i'm making it confusing for people talking about two radios in one post I really should break it up into two!

The crackle is gone and all fixed on the 11-77

The 11-97 has a weak left channel that i'm now trying to fix. It sounds high with very little bass although it is through all the LH speakers not just the tweeter.

Gone over everything with a fine tooth comb and cannot find any shorts or mistakes. Swapped the RH & LH channel tubes and no difference. Tried a spare 12ax7 and no difference.

I initially suspected output trans although I have read they generally either work or don't so it seems the problem could lie elsewhere.

If the valves from the good side make no difference, take some voltage readings. New caps are not infallible.

Still think there is a wiring mistake or short. which could be in the speaker wires?

Walk away & come back to it later.....much later. The hardest thing to spot is one of your own mistakes. Walking away lets the mind reset & you can come back with a different approach.

Marc

I'm off to buy a multimeter and will compare some voltages rh to lh and see if I can't narrow down the variance.

Fired it up today and the left is quite substantially louder than it was? Still quieter than the right though so maybe the fault is a component on the way out but still functioning inconsistently.

Quick question which pins are most important to measure? Both sides of 12ax7 are similar and pms 3 and 6 were the only ones with significant voltage of the 6gw8s and they are all the same.....

In any event I disconnected my sub from the left channel and with a bit of adjustment the Lh channel is sounding much better. May have to see if the problem returns or perhaps the sub was shorting out Lh channel? Either way it's no where near as bad as the other day where the Lh channel was virtually non existent!!

The 6GW8 is a triode/pentode. The pentode section, pin 6 is the anode or plate and should read 300 volts; pin 3 is the screen and should read 250 volts. The triode section plate is pin 9 and should read 130 volts.

12AX7 is a twin triode and the plate pins are 1 and 6. They should read 155 volts.

These figures are from the schematic and I wouldn't worry too much if they are not exact.

As pointed out in another thread, any amp with a push-pull output, such as the 11-97, should have a matched pair of output valves. The 6GW8/ECL86 is a nice tube, but they are rather hard to come by these days.

Thanks mate, pin 6 was exactly 300 and pin 3 was exactly 250! On all 4!

I haven't written down a voltage for the pin 9 I will have to pull out the chassis and check them.

Plate 1 & 6 were both 180v for the 12ax7 does it matter its a bit higher?

Good to know the 6gw8's are spot on.