• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Project: Baldwin Tube Amp...

I haven't been here for a while, but when I was, I was usually in the loudspeaker sections. Anyway...

I have an old Baldwin organ amp which dates back to the mid 50's. It was converted over to stereo operation by Will Vincent a couple years back on the cheap as some kind of deal between him and a mutual friend of my brother's. Well since it was a quick and dirty conversion, none of the original caps were replaced.

A few months down the road, my brother was listening to his system (I was there too), the amp started making very loud ticking and popping sounds through the speakers, so much so the speaker drivers were jumping violently and it scared the pooh out of us! We seriously thought that the speakers might have gotten damaged, but luckily they didn't. However, when it was working, it sounded darn good as I had tried it out on my system for a few days before hooking it up to my brother's system. It blew away the Adcom GFA-555 Mk II amp I had at the time in every way possible.

To make a long story short, I'm planning on recapping this amp to use in my system on my NHT 2.9 loudspeakers. They're rated at 86dB @ 1w/1m and the amp is rated somewhere between 23-28 watts per channel with its P-P 6L6's. The driver tubes are NOS RCA 5751's and it uses not one, but TWO 5U4's. The good thing about using this amp with these speakers is that I now live in an apartment and the speakers never see anymore than about 2-3 watts max, so this old Baldwin amp will be more than enough power.

As for caps, I've got a list...

PS & Filter caps (old 3-section aluminum cans)
(2) 50uF - 100v+
(4) 40-50uF - 450v+

Coupler Caps
(4) 0.1uF - 600v+

Bypass Caps
(2) 100pF - 600v+


When I get some time, I'm going to check all the resistors.


I've found some Xicon 47uF-450v at PE that I think I can use to replace the old 3-section can caps (PS & filter). For the coupling caps, I found the Audiocap PPT Theta caps which get great reviews and are about the most I want to spend. As for the bypass caps, my father has some new 120pF - 400-500v Mica caps that I can use. He said the original Mica bypass caps are most likely good, but I'd rather change them out anyway.

So I was just wondering if you guys had any suggestions or anything for me and this amp. I'm all ears! ;)

Many thanks in advance!

As always, here's a few pics of the amp in its current state...

p782538676-4.jpg


p960503150-4.jpg


p542952352-4.jpg



BTW, all of the tubes tested perfect. I was told the 6L6's are brand new and only used for a couple months.

p224705498-4.jpg
 
Last edited:

taj

diyAudio Member
2005-02-23 8:49 pm
Well, if you can take a couple of clear photos like the second one above, but zoomed in 2-3 times so I can see exactly where everything is connected, I can draw a schematic. you may need to answer a couple questions along the way.

..Todd
 
Well, if you can take a couple of clear photos like the second one above, but zoomed in 2-3 times so I can see exactly where everything is connected, I can draw a schematic. you may need to answer a couple questions along the way.

..Todd

I can certainly do that Todd. I'll take the pics tomorrow morning but will only be able to post in the evening.


good to see you here chops!

Likewise aardvark! Small world, huh? :D
 

taj

diyAudio Member
2005-02-23 8:49 pm
Hey VinylKid, yeah that's why I was curious.

Yeah, Teemuk, that must be it. Or something AWFULLY close. ;) (Saved me from drawing it).

Wave, you mean these? I've got some too. :cool: The photo doesn't do justice to their 'pinkness'.


..Todd
 

Attachments

  • tone-caps.jpg
    tone-caps.jpg
    68.7 KB · Views: 240
Last edited:
So what you're suggesting is that I should test them (which they'll most likely measure good) and leave them in? That would definitely save me some cash, about $24-40 worth depending on which caps I went with. What about those mica caps? My father says those almost never go bad either. These caps are sonically equal to modern "hifi" caps of today?

Like I said, when the amp worked, it sounded really really good, and I've had and/or heard good amps in my system over the years including several vintage SS McIntosh amps, the Adcom I mentioned earlier, a Carver TFM-35x, an Opera Consonance M100SE and a Cary Audio SLI-80. The Baldwin amp gives them all a very good run for their money, and besting most of them!

I guess I should just focus on the PS and filter caps, getting new electrolytic caps to replace them. I'll need six in total. Anything special here or just the normal?
 

taj

diyAudio Member
2005-02-23 8:49 pm
Old electrolytics are probably most in need of replacement. They don't age well at all. And electrolytics have improved a lot in the past 50 years. Nothing special is required but you may have trouble finding much supply of caps in those high voltage values.

As long as those Sangamo's aren't leaking (current, not liquid ooze) and their value is within reason, then keep them. If you want to replace them without entering the snake oil vat, Sprague orange drop (model 715P or better, 716P) are excellent replacements. Antique Electronic Supply sells 716P's for something like a $1.50 ea. Anything more 'boutique' than those is beyond anyone's advice (though such advice is plentiful). Go with your instincts there.

Keep the micas if their value is within tolerance/reason. They've become somewhat more accurate over the years, but they don't deteriorate as far as I know.

..Todd
 
Last edited:
Old electrolytics are probably most in need of replacement. They don't age well at all. And electrolytics have improved a lot in the past 50 years. Nothing special is required but you may have trouble finding much supply of caps in those high voltage values.

As long as those Sangamo's aren't leaking (current, not liquid ooze) and their value is within reason, then keep them. If you want to replace them without entering the snake oil vat, Sprague orange drop (model 715P or better, 716P) are excellent replacements. Antique Electronic Supply sells 716P's for something like a $1.50 ea. Anything more 'boutique' than those is beyond anyone's advice (though such advice is plentiful). Go with your instincts there.

Keep the micas if their value is within tolerance/reason. They've become somewhat more accurate over the years, but they don't deteriorate as far as I know.

..Todd

I'm sure the electrolytics are the cause of the entire problem. As for finding new caps in the high voltages, I think these should work fine for both the PS and filter sections...

47uF 450V Radial Mini Electrolytic Capacitor | Parts-Express.com


If the Sangomo's measure good, then I'll keep them. However, if they don't, you suggest going with the Sprague Orange Drop 716P's? Are those supposed to be better than the current Sangomo's?