Dynaco A25 questions

CT Jim

AK Subscriber
Subscriber
I finally am getting around to a set of A25s but need some input. I typically check all my purchases with an ohmmeter and a 1.5 or 9v battery. The battery just to see if the connections are working.

So, one speaker doesn't pass the battery test until I set the control to the most counter-clockwise setting, however, checking the reading on both speakers I get the following readings..from the most CCW position to the most CW position.

Spk 1 : 7.4, 7.0, 7.1(normal position), 7.4, 6.9
Spk 2 : 14, 7.2, 8.5(normal position), 7.3, 8.9

Both speakers work, although I have not pushed them yet. I did run the control up and down maybe 30 X each, so I'm set at what I'll call +1, because those values are so close. Sound is tentatively ok. I need to clean the control so it works normally.

So these need a little work, played hell getting the first grill off and need the following info. I will reinstall both with velcro later!

I thought of trying to fix these up going thru the slot port, but realize the insulation would prohibit that. I believe the caps are 5.0, so I got some 5.1 from PE, and I need to tighten or replace the binding posts on both speakers.

Is there an easy way to remove the woof from the black goop they used way back? I think that is going to be the hardest part of the whole project!!
 
Not sure on those readings. I'd say theres a chance some of the resistors are out of spec. If I remember correctly theres like 4 or 5 / 2.2ohm and a 10ohm in there. Mine were literally crumbling apart when I got inside. I replaced the 5uF caps with 2 paralleled 2.5uF caps from Erse (pulseX) as well as Erse resistors (they have the 2.2ohm and are low cost). They came out fantastic and are still in use. No, there is no easy way to remove the drivers. I think I actually had the most problems with getting the tweets out. I used an angled machinists pick and slowly pryed them up working my way around numerous times with only very minor damage to the front baffle. Those controls may just be oxidized as well throwing off the readings. Good luck with them; they're worth the effort.
 
So if the woofer is removed to get at the crossover, I assume you removed the tweets because they checked out bad? I can't think of another reason?
 
So if the woofer is removed to get at the crossover, I assume you removed the tweets because they checked out bad? I can't think of another reason?

I actually did a full restoration on them including painting the front baffle. I'm just thorough that's all:D Mine are the Scanspeak version with the vent on top. I even removed the staples from the vent and used stainless screws on it as well as the drivers...they look pretty sweet.
 
Wow, I have to think about this just a tad more. I would typically think the woofer and port would be at the bottom, Unless it was in a position which caused it to be boomy?

Thanks
Jim
 
Yeah the A25 has gone through quite a few different "versions" in its long history. Heres a quick pic. I had some of the crossover, but I can't seem to find em. If I do I'll repost.
 

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I finally am getting around to a set of A25s but need some input. I typically check all my purchases with an ohmmeter and a 1.5 or 9v battery. The battery just to see if the connections are working.

So, one speaker doesn't pass the battery test until I set the control to the most counter-clockwise setting, however, checking the reading on both speakers I get the following readings..from the most CCW position to the most CW position.

Spk 1 : 7.4, 7.0, 7.1(normal position), 7.4, 6.9
Spk 2 : 14, 7.2, 8.5(normal position), 7.3, 8.9

Both speakers work, although I have not pushed them yet. I did run the control up and down maybe 30 X each, so I'm set at what I'll call +1, because those values are so close. Sound is tentatively ok. I need to clean the control so it works normally.

So these need a little work, played hell getting the first grill off and need the following info. I will reinstall both with velcro later!

I thought of trying to fix these up going thru the slot port, but realize the insulation would prohibit that. I believe the caps are 5.0, so I got some 5.1 from PE, and I need to tighten or replace the binding posts on both speakers.

Is there an easy way to remove the woof from the black goop they used way back? I think that is going to be the hardest part of the whole project!!


Double check the crossover cap value, I've heard some of these had 8 uF caps.
 
and heres what you will be looking at, before and after cap replacement
 

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There is a bit of difference as my pic shows. My woofer and tweeter placement are reversed?? I also posted a pic of the crossover, which does have the 5.0 caps.

Tcom
looks like you left the original 2.2 ohm and 10 ohm resistors, and only replaced the cap? I can clean the rotary switch now, but is it necessary to change out the other pieces besides replacing the the 5.0 caps??
 

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I say its at least good to test em while your in there. You'll always wonder if not:yes: I only replaced mine because as I said they were literally crumbling apart.
 
Mine are not crumbling that I can see. I will clean the rotary control and recheck the readings. Can these 2.2 ohm units be measured in circuit?
 
Mine are not crumbling that I can see. I will clean the rotary control and recheck the readings. Can these 2.2 ohm units be measured in circuit?

Probably not very accurately, but whats a little more solder. Most likely they're fine, I've just gotten into the habit of replacing resistors when I do a speaker recap. They're cheep unless your using mills, and I get peace of mind. I may be in the minority though.
 
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