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Beveridge S2 OTL power amps...Help!

Blue Shadow

Blue Shadow

Waiting for Vintage Gear from this century
I have posted a bit about this CL pick up yesterday and thought that before anything the amplifiers need to be checked out. Here are some pictures of the amps, one for each speaker used as a base of that speaker with the speaker slotting into the amp with two guide pins and 5 banana plugs per speaker.

I have already posted these two pictures. The first one showing the tubes and the missing oily/sticky capacitor I had questions about (posted in DIY) that was just above the two left tubes. I've cleaned this cap, .10µF/4500V dated 2/76 and will see what is up with it.

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The cloudy tube is cracked around the base and I have been contacted about a possible replacement. I still need to open the second amp.

I want to do this safely so I would appreciate comments on discharging the caps. What I did with the first amp was connect a few wirewound resistor to chassis ground and then clipped onto each capacitor end. I then touched this resistor thing to each end of the capacitors. I don't know the last time these were powered and don't need to be introduced to as much as 3200 volts (valued noted on the circuit board). I'm learning to work with one hand behind my back.

After making the amps safe, I will get them cleaned up, repaint the bottoms (the part not on the amp shown open) and then evaluate some components, get the power wiring safely attached and hope for the best. I'm going to contact Beveridge to see if a schematic is available.

Not being a tube tech of any kind, I'm open to suggestions on proper power up (10A variac and DBT available).

Any help is greatly appreciated. I'm going to detail the bottom panel now. It is cleaning and spray painting. I can handle that part.
 

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Are those amps, or the high voltage supply for the electrostatic tweeters? Or is it somehow doing both functions?

If its an amplifier, I'd really consider replacing all 4 of those tubes, or at least having them tested to verify condition. Not sure where you are in SE PA, but I'm in New Jersey, about 50 minutes from Center City Philly. I'm planning a trip up to Atco on Saturday, and will be driving by the Philly area bridges on my way home. If you'd like, I can swing by with my tube tester, assuming it'll test those particular tubes. If that would be helpful, let me know what the tube numbers are so I can check my scroll chart.
 
Those should indeed be both the amp, and the HV panel bias supply for the speakers. 3200v would be too high, except for panel charge.

Are those 6LF6 output tubes? It does look like one of them has lost its vacuum, in any case (the far right big tube in the picture)... that will need to be replaced.

Regards,
Gordon.
 
4-36KD6 tubes per box, one box per speaker and as Gordon states it is panel bias and amplifier. The input is the AC and a preamp output. Input is labeled 1V 47kΩ and is an RCA connection.

I'd be happy to have you swing by and check these out. I'm in West Chester very close to 202. A bit out of your way but maybe it will be worth it. Come take a listen to some other stuff since I have more work to do on these.

The 36KD6 can be replaced with a 40KD6 and one of the tubes in the other amp is dual labeled. I have a trio of tubes coming in from a known tube equipment collector here on AK. One is NOS so if a tube tester can measure these tubes we will know the readings of a good one.

I talked to Rick Beveridge today and he said it is good to use matched pairs (performance-wise) for these amps and not to mix new and old. It would be good to see what I have as far as tube performance is concerned.
 
oh, West Chester. I pass through there often on 202. A friend of mine lives near Pottsville, and I take a ride up there once a month or so. My route takes me up 202 for part of it.

May or may not be at Atco, mostly it'll depend on the weather. If I don't go, it means I've got the day free so I can still take a ride up that way. My tester isn't the fanciest thing. Its an old Eico 667, but it should pull out obvious faults and see if the tubes are useful at all. I'll check the scroll chart on it tomorrow, but I'm reasonably sure it should check those. PM me your phone number or whatever and I'll try to figure something out.
 
Things are moving forward on this project. As I try to learn about the amps, collect documentation (schematic) if available, I have time to take the speakers apart. Fortunately, the Beveridge site has a step-by-step dis-assembly 'tribute' post that details how go get inside. Electric screwdriver is highly recommended.

The insides of the speakers look very good. I was told that although these speakers work, there is a buzz in one of them, most probably due to dirt on the electrostatic element. The speaker has three elements and the backs are clean. The acoustic lens you can see in the picture with the panel removed is what makes these speakers fill the room with sound. The dirt on one of the panels is the deteriorated foam from the grilles. It looks like I will have to pull all 6 panels and carefully clean them of this foam.

This will be plenty of work while I learn more about the amps and figure out what to do to them to make them safe and properly operational.

Here is a link to a picture of the 1 and II. The ones I'm working on are the II and they sit on top of these amps which are not shown in the picture.

http://cpskal.gr/forum/printview.php?t=1855&start=0

These speakers fit nicely between the wheel wells of my neighbors Ford pick-up. Why he bought and F-250 I don't know but with the speakers loaded, I was able to put the hard cover back down on the bed, keeping the speakers out of the wind.

I'm looking forward to hearing these.
 

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Things are looking up for these amps/speakers. Gadget73 stopped by today shortly after the three 36KD6/40KD6 tubes showed up from Ohighway (thanks). The one NOS tube tested to 130 and the others were 112, 112, 110, 110, 110, 102, 98, 82 and 84. This means I have a full complement of tubes for the amps and can start evaluating the caps for replacement.

Lytics will be replaced when the amps work if they test decent. 47µF is not hard to test with meters and after cleaning the amps I'll bring them up slowly and see what happens.

I received a schematic that may be for the later 2SW speakers but it is something to start with to compare with what I have. So things are coming together on these.
 
Very cool project !!

Blue Shadow said:
I have a trio of tubes coming in from a known tube equipment collector here on AK.
Click to expand...

Lol...

Blue Shadow said:
The 36KD6 can be replaced with a 40KD6 and one of the tubes in the other amp is dual labeled.
Click to expand...

Just to satisfy my curiosity, one of the used tubes I sent was marked 40KD6. What was the tester reading associated with that one ? Since some have the dual markings, I'm having a hard time believing there's any actual difference between the 36kd6 and 40kd6.
 
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The how I got these thread is in $&¢: http://audiokarma.org/forums/showthread.php?t=425742

The tubes that also indicated 40KD6 were tested as follows: the used Raytheon 84, one 77-04 GE 112, 102 and 110, and the non-legible one 112. The GEs are labeled as both types but only etched as 36KD6. The non-legible is etched with both types. The Raytheon was the 40KD6. So it seems you are correct that there is not really a difference in these tubes.
 
Well, wouldn't have looked here for the Beveridge updates, but great to see an AKer got them! A small Beveridge family here on AK.

Can't wait to hear more impressions and see additional pics. Best of luck with the project.

:lurk:
 
I checked my Sams tube substitution manual. According to that you can sub a 40kd6 for a 36kd6, but not the other way around. So maybe there is a difference but for your application, jamming a "40" in a "36" circuit, maybe the functional difference is minimal ? :dunno:

Blue Shadow said:
The tubes that also indicated 40KD6 were tested as follows: the used Raytheon 84, one 77-04 GE 112, 102 and 110, and the non-legible one 112. The GEs are labeled as both types but only etched as 36KD6. The non-legible is etched with both types. The Raytheon was the 40KD6. So it seems you are correct that there is not really a difference in these tubes.
Click to expand...
 
Oh, if anyone was curious about the test numbers on the tubes, those are percentage numbers from an Eico 667 tester. Its been rebuilt and calibrated as best I can from info found online. I didn't do the plate current test mod to it though, so no testing done for that.
 
Lucky you.... I was gonna run a quick check on them on my Hickok 539c before I shipped them out and..... surprise. No listing on my roll chart for those. :sigh:

gadget73 said:
Oh, if anyone was curious about the test numbers on the tubes, those are percentage numbers from an Eico 667 tester. Its been rebuilt and calibrated as best I can from info found online. I didn't do the plate current test mod to it though, so no testing done for that.
Click to expand...
 
Ohighway said:
I checked my Sams tube substitution manual. According to that you can sub a 40kd6 for a 36kd6, but not the other way around. So maybe there is a difference but for your application, jamming a "40" in a "36" circuit, maybe the functional difference is minimal ? :dunno:
Click to expand...

One would lose a little bit of emission running a tube with a 40V filament at 36V; the converse would put 40V on a 36V filament; not a good idea - at best, it would shorten the life of the 40V tubes (possibly significantly).
 
Ohighway said:
Lucky you.... I was gonna run a quick check on them on my Hickok 539c before I shipped them out and..... surprise. No listing on my roll chart for those. :sigh:
Click to expand...

Its not on my roll chart either, but I was able to find an updated roll chart online somewhere. Its printed out on regular paper. Not nearly as convenient as the real thing, but its better than nothing.
 
Of course you mean "it would shorten the life of the 36v tubes".....

That would certainly be my understanding. Conversely, running 40v tubes on 36 might make for looooonnnnng life. Maybe.

I wanna' hear more from Keith about the progress !

mhardy6647 said:
One would lose a little bit of emission running a tube with a 40V filament at 36V; the converse would put 40V on a 36V filament; not a good idea - at best, it would shorten the life of the 40V tubes (possibly significantly).
Click to expand...
 
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Funny thing- the "latest" RCA tube manual (RC30) gives the exact same specifications for the 36v and 40v tubes.

I wonder if after a while, they just consolidated the manufacture into one type?

Obviously, they didn't think there was THAT much effective difference, in life-span expectation or loading...

Regards,
Gordon.
 
At least one of those tubes had both numbers printed on it. My tester setup is identical for both, 35 volts on the heater. Of course my selection at that range goes from 35 to 50, which is obviously too much.
 
Ohighway said:
Of course you mean "it would shorten the life of the 36v tubes".....

That would certainly be my understanding. Conversely, running 40v tubes on 36 might make for looooonnnnng life. Maybe.

I wanna' hear more from Keith about the progress !
Click to expand...

The first number is not always the heater voltage. For example the 7N7 is a 6.3V heater.

Edit: I stand corrected. TDSL Tube Data shows the 36KD6, 30KD6 and 6KD6 as subs for 40KD6 with different heater voltages.

If you ran a 40V tube on 36V heaters it would not have rated emissions.

I have a lot of emissions myself and my wife complains often....:thumbsdn:
 
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