Dynaco electical problem? Please help!

[Horswispr]

I've had close to 20 pair of Dynaco A-25s pass through my house over the past year. All have been acoustically perfect, with the exception of one clearly blown woofer. Fortunately, the seller of that pair was cool, and took them back. I didn't want to bother searching out and replacing a woofer. I am really good at making the wood surfaces look beautiful, but I'm not an expert when it comes to the guts (I don't own a soldering iron right now). Recently I bought a pair of A-25s on Ebay that looked terrible, as expected, but I noticed that one tweeter's level was WAY below the other's. I did some experimenting with another Dynaco tweeter I had on hand and came to the conclusion that the new tweeter itself was OK. So, thinking oxidation, I wiggled the wires at the back of the new tweeter, and also removed the woofer (keeping it attached--no soldering iron) and wiggled the wires where the tweeter leads enter the crossover network. Lo and behold, the tweeter performed normally once I put everything back together again. For awhile. A couple of times, I thought I heard drops in level, followed by spontaneous returns to normal. My question is: Does this sound like a wiring/oxidation problem? Or could there be a problem in the crossover network itself? They sound fine right now, but I wouldn't want to move these along to someone else unless I was sure they were functioning 100%. Thanks for any words of wisdom!

[dynaco_dan]

Hi there;

I would suspect from your description, that perhaps a solder connection on the the crossover end, was not 100% perfect.

You would need to have just the tweeter operating and carefully and gently check the crossover wire connections again.

[Horswispr]

Thanks, Vern.

--Colin

[Pete B]

It sounds like a cold solder joint, it would be wise to heat and reflow all the solder connections with a small amount of fresh solder. Might as well also apply a contact cleaner to the switch contacts.

[soundminded]

Intermittent problems are often the hardest of all to diagnose and cure. Just when you think you've got it fixed and everything it put back together again, it comes back and frustrates you. I had this happen recently with my car and had to pay the dealer $300 for several house of labor to find a bad $8 spark plug. The only advice I can give you is that it helps if you can find out what you have to do to make the problem happen whether it's wiggling a wire or a jiggling a tweeter level control. If you can't use a soldering iron or a volt meter, get help from someone who can.

BTW, the replacement woofer for Dynaco A25 is Seas model 25F-EW (HO85) and is available from Madisound. In the most recent catalog I have from them, it's $65.80.

[dynaco_dan]

Hi Colin;

You did your own troubleshooting.

You just didn't realize what you had found.

When you mentioned you wiggled the wire near the crossover, you very likely either, pulling on the switch contacts or a poor solder connection or the tweeter drive connection.

Because the tweeter started working, you know and we know, that there is very possibly a solder connection problem.

Because we cannot see all that you are doing, or feel your gentleness, there is not too many possible bad connections.

As far as buying replacement drivers, ebay is just one source for a used driver, rather than a more efficient new one, is my suggestion.

[Horswispr]

The problem turned out to be near the capacitor, which appears to be in the tweeter circuit only. I moved the cap around, heated up the connections around it, and it's been good since. I'll listen for several months to make sure the connection stays good before I move this speaker along.