Hacker AL42 Smoothing Cap Voltage Reading

[PJay1966]

Hi Graham

The original is not a wirewound it looks like an old carbon film. I mentioned wirewounds as I had some in my spares box of the right 200ohm rating.

[ms660]

I think the original was a carbon 2 Watt job.

Lawrence.

[PJay1966]

Originally Posted by ms660

I think the original was a carbon 2 Watt job.

Lawrence.

Sounds about right, a 10W wirewound is overkill but I think it should be ok to use, what do you think?

[ms660]

Originally Posted by PJay1966

a 10W wirewound is overkill but I think it should be ok to use, what do you think?

It'll do fine.

Lawrence.

[PJay1966]

Thanks All

Thought I would post a quick update in the hope that someone can point me in the direction of a new problem.

What I have done so far on my AL42:

1 Replaced the 4 50uf caps with new axial electrolytics
2 Replaced a number of resistors some of which were way out including the 200ohm smoothing cap resistor which read 320ohms
3 Cleaned the unit and all the pots (with Servisol)

The original hum problem is greatly improved its barely noticeable even at full volume, which is good! However I have noticed that if I turn the bass pot towards max the unit emits a quite load buzz which disappears when the bass knob is turned down. Now, I have noticed that the ECL86's are not a matched pair one is a Mullard the other is a pinnacle and examining them it looks like their construction is slightly different. Before I sink a good amount of cash on a new pair of ECL's I wanted to check with the forum if mismatched valves could be causing this issue or should I check something else?

Thank you as always I am really grateful for any guidance offered...

[BRASSBITS]

have you got the GP42 Gondolier if so swap their valves round and see what happens

[Chris55000]

Hi!

Most of the 350V rated electrolytic capacitors used in valved equipment actually have a "surge" rating of 400/425V (often marked on the can!), so 358–365V at the cathode of the rectifier should be no problem!

The usual cause of hum from ECL86 valves is a "hot leak" that occurs across the mica supports for the electrodes of the pentode section, this causes the valve to develop grid–current leakage that causes a rise in the anode and screen currents when the valve getts hotter, causing more ripple on the h.t. line and hence more hum!

My experience with ECL86 valves is that running them under "EL41" conditions with a reduced pentode screen voltage of 210 V and a 220 Ω pentode cathode bias resistor does tend to improve the reliability of these valves!

Chris Williams

[Outposter30]

Originally Posted by PJay1966

Still working on this AL42 and just been testing components. I have found that the smoothing cap resistor which should be 200ohms is reading nearly 300, certainly out of tolerance in my view. I have a few 10W 200 Ohm wirewounds which I think I may swap the old one with does that sound reasonable?

Is that resistor before or after the smoothing cap...

If it's before the cap, then chances are the cap is leaky under operating voltages. If it's after the cap, then something downstream from it has/is drawing a lot of current through it...

[AD360 Rob]

Am I right in assuming that the AL42 is not connected to anything on its input side? If so, the hum/buzz you are getting seems to me to be normal open circuit input buzz. Have you tried it with the record player connected?

[PJay1966]

Yes I have and it sounds really quite good. There are however two faults one a buzzing at loud volume and the buzz when the bass knob is turned up the sound otherwise is better than I expected.