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Old 30th July 2013, 02:38 PM   #11
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Phew! At least the XFMRs are still there. You may want to leave them as is only redo the covers with black paint. Must be local production as Philips never used transformer covers.

It looks like someone already had a go at it. The black caps are not original, nor is the white ceramic resistor. The green resistors with the value printed on them are also not Philips but prolly original. The mustard capacitors are famous and original as are the blue electrolytics. The resistors in the power supply look tired and should be replaced. Can't figure out the GZ34s (parallel or something else?). Oh, and all caps on the top side of the chassis (big cans) will be toast.

A shot from the front panel would help, as some more closeups. The cover over the tone control (ECC83, prolly standard Baxandall) is in the way as well. And the EF86 preamp is completely hidden by the shielded volume control (at least I think that's what it is). Oh, stick to one amp when you make more piccies. The better looking one...

Last edited by Regenpak; 30th July 2013 at 02:40 PM.
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Old 8th August 2014, 03:55 AM   #12
apnneto is offline apnneto  Brazil
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After awhile, I'm back to this project. I thought it was a Mullard 5-20 mod, but after drawing the wiring diagram from the circuit, I know that this is not the amp.
Some days ago I was starting to work on a ground plan, and then I had to stop.
Now I'm totaly lost. I searched the net looking for similar schemes and informations about this amp but had no success.
So, I have several questions, like these:
  • What type of source can I connect in the audio inputs? Too much gain ???
  • Is it better than Mullard 5-20? Or should I forget it and go with 5-20?
  • How the pots connected to 'line in' on EF86 works? Are they like a mixer?
  • The original output transformer was 800 ohms. One was broken. I'm using a spare pair with 4/8 and 16 ohms. How should I modify the feedback loop?
Well, the only thing I can do now is drink a beer ... by the way, I will check the schematic ... may be I draw something wrong ...

More photos here.
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Last edited by apnneto; 8th August 2014 at 04:12 AM.
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Old 8th August 2014, 06:19 AM   #13
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You have an unique amplifier, imo, you should not modify it to Mullard or anything else, it should be restored (sans the OPT) to the original condition as much as possible. Is there a model number shown on the front plate (on the box containing the EF86)? Also, what are the control functions on the front panel, from left to right? Since the OPT is gone, you are free to re-configure the output to work with modern off-the-shelf one - but it's still going to be a big one though. How much power do you need?

Last edited by jazbo8; 8th August 2014 at 06:24 AM.
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Old 8th August 2014, 10:17 AM   #14
okcrum is offline okcrum  United States
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There seem to be some missing connections around V8B on your schematic. I agree with restoring the amp rather than modifying it.
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Old 8th August 2014, 01:28 PM   #15
Ketje is online now Ketje  Belgium
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The inputs seems to accept two sources with one vol.cotrol.Nothing in the middle ,one direction for each source.
In the bottom the two inputs have something like a (adjustable) phantom supply.Very sensible, condensor-mike ?
There are some errors in the schematic but make not to much about it,Herman Karton make them too .
I indicated with a red "circle" where I found something wrong.
The use of the two Si-diodes is not very clear.
Mona
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Old 8th August 2014, 01:30 PM   #16
Ketje is online now Ketje  Belgium
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Now here is the schematic with my suposed adjustements.
Mona
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Old 8th August 2014, 01:46 PM   #17
apnneto is offline apnneto  Brazil
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Quote:
Originally Posted by jazbo8 View Post
You have an unique amplifier, imo, you should not modify it to Mullard or anything else, it should be restored (sans the OPT) to the original condition as much as possible. Is there a model number shown on the front plate (on the box containing the EF86)? Also, what are the control functions on the front panel, from left to right? Since the OPT is gone, you are free to re-configure the output to work with modern off-the-shelf one - but it's still going to be a big one though. How much power do you need?
I thought about Mullard 5-20 because there are a lot of information out there and the tubes are all the same, as the power transformer. But for this unit I know nothing.

I think it was used as a PA on a cinema or theater. The inputs are microphone, pickup and two source in for audio projector. But I know nothing about this circuit and the quality of the sound.

But as you suggested, I will try to restore to its original condition.

There is a model number but I tried to find any information about them with no success. The model is Philips type 3860/24, serial number 192, 275 watts.

The controls on the front, from left to right, are:
  1. Volume control for output EF86 and connection to ECC83;
  2. Switch from Mic/Pickup Input (down) and line 1 and 2 (up)
  3. Volume control for inputs Mic/Pickup (half for each one)
  4. Treble
  5. Bass
  6. Power On

For power output anything between 50 and 75 watts are welcome. I will probably buy a pair of OT for UL use.

I'm still trying to find reviews for this circuit.
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Old 8th August 2014, 01:47 PM   #18
apnneto is offline apnneto  Brazil
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Quote:
Originally Posted by okcrum View Post
There seem to be some missing connections around V8B on your schematic. I agree with restoring the amp rather than modifying it.
Your are right! Thank you.
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Old 8th August 2014, 01:53 PM   #19
apnneto is offline apnneto  Brazil
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Quote:
Originally Posted by Ketje View Post
The inputs seems to accept two sources with one vol.cotrol.Nothing in the middle ,one direction for each source.
In the bottom the two inputs have something like a (adjustable) phantom supply.Very sensible, condensor-mike ?
There are some errors in the schematic but make not to much about it,Herman Karton make them too .
I indicated with a red "circle" where I found something wrong.
The use of the two Si-diodes is not very clear.
Mona
Thank you for your help.

I will make the adjustment. And you are right about the vol. control: one direction for each source, but this is true only for Mic/Pickup (the two source in on the bootom). For EF86, the output is connected to one vol. control.
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Old 8th August 2014, 02:03 PM   #20
apnneto is offline apnneto  Brazil
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Quote:
Originally Posted by Ketje View Post
Now here is the schematic with my suposed adjustements.
Mona
Very good, thank you a lot.

I will turn on one monoblock e measure the voltage and check with your values. They seem to be very close.

The feedback resistor is 33k (330k was wrong as the r22 that is 68 ohms/50w). But it was projected for 800 ohms at the output of OT. Now, which value should I use?

About the input of EF86, what kind of source can I connect? I tried a CD input with a passive preamp but the gain is too high. Is there any mod that I can do to get better results?

About diodes, I included them as suggested on post #3.

I'm now working on the schematic!

Last edited by apnneto; 8th August 2014 at 02:06 PM.
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