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Old 3rd January 2018, 12:15 PM   #31
cnpope is offline cnpope  United States
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I have one, which I built several years ago. It has been extremely reliable and performs excellently.
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Old 3rd January 2018, 03:49 PM   #32
smoking-amp is offline smoking-amp  United States
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I would not expect to need women with shopping-carts of tubes for hourly repairs. This is far smaller than EINIAC (20,000 vacuum tubes).
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I have one, which I built several years ago. It has been extremely reliable and performs excellently.
I was speaking of the case of 600 12B4 tubes to obtain a quality 5X rp load line for the triodes.
That would be 1200 tubes for a stereo amplifier then.
The Tim Mellows OTL is using two BIG tubes per channel.

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I commend the book Hot Air Rises and Heat Sinks, which discusses why many heat problems confound average persons. In particular, putting hot-spots together may *improve* cooling; or at least not get you in trouble.
One needs a "chimney" effect to improve air circulation with more heat. The MP amp has got the tubes on a flat plane, their density impairing easy air flow.

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Bootstrapping the driver to "equalize" the drives may be another complication avoided. Work out the gains. The "plate loaded" side has very low gain. The "cathode loaded" side has lower gain, but maybe not enough to hurt, or justify all possible "improvements".
The gains would be around 3 bottom side (Mu 6.5 swamped by overloading) and less than 1 top side (cathode follower). An excellent 2nd harmonic generator I think. It would only take 2 resistors (the Futterman fix or the Technics "anti Futterman" fix) to fix this. This -could- be a "tube sound" choice by the designer. Not good for the already stressed tubes though, making them run hotter. The choice of using more tubes than Futterman's H1 does allow the use of reduced N Fdbk, but mis-matching the tube bank gains requires increased N Fdbk.

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Bigger tubes mean less tubes but they cost more each.
It's not just socket wiring. Where are the bias adjustments for all those tubes? I only see one for the whole bank. So matched tubes are required there. I would be a really "pi__ed" customer if I had to order 60 matched tubes every time a few went out. It does look like all those tubes were ordered as a single batch from Raytheon. All it takes is one of those tubes to short out, and good-bye speaker.

If there really was some "military" aspect to this guys work, I would guess the CIA were planning to send this thing to "der Fuhrer", so he would be totally occupied with maintaining his sound system.

OK, anti high tube # OTL rant off. Some significant amount of TLC can likely bring back some nice sound. A few fixes might make good sense.

Last edited by smoking-amp; 3rd January 2018 at 04:06 PM.
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Old 3rd January 2018, 10:30 PM   #33
cnpope is offline cnpope  United States
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Originally Posted by smoking-amp View Post
I was speaking of the case of 600 12B4 tubes to obtain a quality 5X rp load line for the triodes.
That would be 1200 tubes for a stereo amplifier then.
The Tim Mellows OTL is using two BIG tubes per channel.
Yes, my reply was to TonyTecson's question about the Tim Mellow OTL.
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Old 3rd January 2018, 10:37 PM   #34
TonyTecson is offline TonyTecson  Philippines
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and Don was responding to PRR comments.....
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Old 3rd January 2018, 11:14 PM   #35
smoking-amp is offline smoking-amp  United States
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Yes.
Well we all look at things differently, so all opinions are always of interest. And I value PRRs comments fully as well. I just happen to be more economical and reliability minded about designs, 100 parallel 12AX7 tube amplifiers do get under my skin, for example. Some designs are obviously more about climbing Mt Everest, than about practicality. I would put the MP amplifier somewhere in the neighborhood of the old Chinese proverb: "May your journey be interesting." (never a dull moment)

Last edited by smoking-amp; 3rd January 2018 at 11:37 PM.
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Old 3rd January 2018, 11:35 PM   #36
TonyTecson is offline TonyTecson  Philippines
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that is alright Don.....it is really the journey more than the final destination where the thrill is at...the journey is where we pick up lots of gems along the way...
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Old 4th January 2018, 08:38 PM   #37
kasanay is online now kasanay  United States
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Originally Posted by Carlp View Post
Pictures??? (of the Bozaks in particular)
Here are some shots of the Bozak Speakers. The are wired to present a 32ohm load.
Each cabinet contains:
(4) 12" woofers
(2) 6.5" mids
(8) 2.25" tweeters
(1) Jensen 302 super-tweeter
(2) crossover networks
Attached Images
File Type: jpg System.jpg (572.1 KB, 253 views)
File Type: jpg Woofers.jpg (657.4 KB, 249 views)
File Type: jpg Mids.jpg (575.4 KB, 245 views)
File Type: jpg Tweeters.jpg (725.7 KB, 240 views)
File Type: jpg Xover Network.jpg (715.1 KB, 243 views)
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Old 5th January 2018, 01:28 AM   #38
Carlp is offline Carlp  United States
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Wow! Thx for the pics! They look to be in fabulous shape.
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Old 5th January 2018, 01:49 AM   #39
kevinkr is offline kevinkr  United States
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Definitely going to be fun once you get it operational. I'm pretty sure the turntable is not original.
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Old 6th January 2018, 04:17 AM   #40
smoking-amp is offline smoking-amp  United States
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The speakers look really nice!

Just tossin' an idea out here: You are apparently short of 12B4 tubes to fill all the sockets, and buying new ones would require 60 new matched ones.

You could use all the tubes you already have to form the upper banks of each amplifier (after testing the tubes). This could even be re-configured to use the FULL 30 sockets for each upper bank. One could also use every other socket then to double the inter-tube spacing.

For each lower bank, use one or two 26LW6, 40KG6, or 26LX6 tubes. Some gain adjustment would be needed to match the upper and lower banks then. Screen voltage for the bottom pentode bank would be ground based, so easy to derive. Just an idea. Cheaper to do. Try on one amplifier 1st.

Optional idea:
Get a 4:1 OT to put between the amplifier and speaker. This could be just an industrial 480V to 120V xfmr to try it out. Would raise the tube loading from 32 Ohms to 512 Ohms. The triodes won't have enough voltage headroom to go to full power at 512 Ohms however. Going to 6LW6 etc top and bottom would bring back the full power rating.
Attached Images
File Type: jpg 6LW6_curve.JPG (292.5 KB, 80 views)
File Type: jpg 6LW6_curve2.JPG (400.2 KB, 23 views)
File Type: jpg 6KG6_curves.JPG (307.7 KB, 21 views)
File Type: jpg 26LX6_curves.jpg (224.7 KB, 22 views)

Last edited by smoking-amp; 6th January 2018 at 04:46 AM.
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