Armstrong 626 troubleshooting problem

[audiogymp]

Hi Pablo

Thanks for the follow-up. I'm still waiting for the transistor to arrive. I'll be sure to let you know once I have it. Good to know you are still on the line.

Cheers, Jon

 

[audiogymp]

I got fed up waiting for the transistors from China. I had some components for a Mouser order, so I added a 2N5320 for this amp. Should be here in a week.

 

[6taafondo]

Did not received last message notification from the forum. Just checked out the thread and found it. So you must be about to getting hold of that elusive parts, Jon.

 

[audiogymp]

Mouser delivery tracking indicates that my order has reached Melbourne, so it should be delivered in the next day or two.

Cheers, Jon

 

[audiogymp]

Hi Pablo

The 2N5320 seems to have done the trick and I suspect that it may have been causing problems for some time. Quiescent current across the four resistors is now more stable and consistent for the two resistors on the same channel. I got them all set within a few mV. The drivers get reasonably warm and temperature seems to affect quiescent current, so I suspect there will always be some variability.

Interestingly, once I installed the transistor, the receiver started tripping the earth return on the house fuse box. It did this twice in a short space of time. I disconnected the earth line from the three-pole capacitor across the power switch, as you recommended and the problem stopped. It's interesting that this re-emerged once the power stage was repaired because it hadn't happened for a while. But I have had the receiver running for two days now without any recurrence.

I'm now doing the lap of honour (replacing lights, the two outputs that hadn't failed and cosmetics to the wooden casing). Should be finished soon.

Thanks for all you help and for sticking with me to the end.

Cheers, Jon

 

[6taafondo]

We really did narrrow it down, Jon! Congrats on finally getting it running; trully glad about it. If you notice it's warming up too much, reduce bias, very slowly, giving much time for temperature to accomodate.

Post a picture of it once finish.

Pablo.-

 

[audiogymp]

Hi Pablo

Here are a couple of snaps. The first at night to show the face lights. The second during the day show the wood, which has come up nicely with a little sanding and oil. There was a bit of rust, which responds well to WD40. The resolution is not quite as good as I hoped but I think you will get the idea (I can take some better shots if you like). It has come up looking almost new but it's missing the logo on the left side of the face.

At first I thought I had a problem with the FM section because one channel was a bit quieter and dull but it turned out to be the AM/FM selector switch. Not sure if it is the contacts or the mechanics of the switch but I will need to continue working/cleaning/lubricating it to get it working properly. Apart from that, it has a smooth but lively sound - quite pleasing. Needs reasonably efficient speakers but is able to produce some volume and good bass.

Thanks again for all the help.

Cheers, Jon

 

[6taafondo]

Wow, really beautiful. You did a great job on it, Jon! Fine piece of equipment.