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Amplion Amplifier

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I have a valve amplifier I obtained back in about 1972 when I was an apprentice. It ‘was’ working but has sat in a drawer for many years and I recently unearthed it in order to get it working again.
It bears the name ‘Amplion’ and consists of a steel chassis with a steel case. It’s mains operated, through a transformer – no earth!
There are two channels, marked I and II and outputs on the rear for 3 or 15 Ohm speakers for each channel. Each channel has its separate Volume and Tone controls.
Each channel consists of an EBC90 driving an EL84 with a single-ended transformer. However, there is a two position rotary switch – Monaural/Stereophonic.
Having traced out the circuit, it is apparent that the rotary switch (6 poles) transforms the configuration from two independent single ended channels into a single monaural amplifier with an EBC90 amplifier, EBC90 phase splitter and two x EL84, now in push-pull class AB. (One of the output transformers has an additional primary for this connection).

I'm guessing it dates from the mid 50s or 60s.

Does anyone have any info on this amplifier or, indeed, anything on Amplion?

(I’m aware that there is a more modern company using the Audiffex Amplion name for software related products but I guess they're unrelated).

Thanks,
Graham.
 
The EBC90 seems to be like the 6AV6/EBC91, where the triode resembles those found in 6SL7s and 5751s.

There's nothing to stop you from installing a proper, 3 wire, safety grounded, power cable and (if necessary) isolating signal ground from the steel chassis.

L_RD knows that all sorts of suitable schematics are available to you. Therefore, exact knowledge of the OEM circuitry is (IMO) not essential.

FWIW, I'd put a pair of identical O/P trafos in. Source something along the lines of Edcor's GXSE15-5K, which allows for UL mode "finals", closer to home. Magnetics are heavy and shipping them long distances is costly.

Please post some photos of the innards and a description of the B+ PSU.
 
Hi Eli - thanks for the suggestions. The circuit is now posted - complete. The rotary switch has 6 x changeover poles and is shown in the 'stereo' position.
I'll certainly include a chassis earth in the rebuild and also post some pictures of the internals (as was) and when it's finished.

Thanks,
Graham.
 

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Graham,

I think you can squeeze a bit more out of the unit. For starters, I see no NFB, which with full pentode "finals" means very poor damping factor and all sorts of distortion. :mad:

Consider SS rectified B+, a proper CLC PSU filter, Russian 6П14П-EB (6p14p-ev) [AKA EL84M] O/P tubes, and regulated g2 B+. Put 2X 0A2 gas discharge regulators in the 7 pin mini sockets and a 12AX7/ECC83 in the socket currently occupied by the EZ81/6CA4 rectifier. The 6П14П-EB is a very tough 7189 equivalent. With 300 V. on g2, as long as plate dissipation is held to 12 W. you will be just fine.

Frankly, about the only thing I find impressive in the schematic is the 150 mA. EZ81/6CA4 rectifier. The power trafo may be decent, since they would have used a 90 mA. 6V6/EZ90, if they could have gotten away with it.
 
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This kind of mono/stereo switch does remind me of some early stereo radios. Tube lineup is certainly from a radio, also the EZ81 was the most popular and probably cheaper rectifier on tube radios of the time. This amplifier may have been built by a radio manufacturer. I have restored a Loewe-Opta tube radio built in 1959 that also has a switch to reconfigure the output stages between SE stereo and PP mono. It basically was a standard mono radio with a marketeable "future proof" option. As stereo device, they don't even tried to make it technically sound. It had a lot of hum (inudible in PP operation - I had to install a 1H filter choke just to make it bearable) and it was a pain to troubleshoot due to the complex switch and associated bundles of wire that made the output stage prone to oscillate.
If the collector value of this Amplion is low, I guess that a total rebuild as true stereo unit is the best option. Before committing any serious money to the project, I would try a minimal restore (recap, deoxidation...) to check if the transformers are still good after 30-50 hours of operation. Sometimes the insulation is degraded because they were undersized and become too hot, and after many years of inactivity the insulation finally breaks down.

Edit: I just checked on radiomuseum.org (the proper site to post pictures and schematic of old radios and amplifiers), and indeed there is a GB radio and speaker manufacturer called Amplion that was active up to late '50.
 
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Thanks pcan - interesting stuff. I've stripped the amplifier internally and cleaned the chassis up and I'm wiring heaters at present - dual wired this time as one side relied in the chassis earth originally. I'll build it as a pure stereo initially and, as you suggest, check the integrity of the transformers.
I'd like to keep it as original as possible but it'll need some new components. It'll be interesting to see how it performs!
I've sketched out the separate Mono and Stereo configurations. The power supply is in the original circuit a couple of posts up...
Thanks, Graham.
 

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If you will get too much hum on the stereo configuration, you may keep the EZ81 and replace the 3W dropping resistor in the power supply with a inductor such as RS part number 2508972543 (Triad Magnetics C-24X) and increase to 33-47uF the second filter capacitor; or you may replace the EZ81 with two C3D02060G (RS part number 809-9045) and increase the value of both filter capacitors substantially. The special Schottky diode is a suggestion I got on a previous Eli Duttman post and it sounds nice indeed. If you need more data, there is a free software called PSU Designer II to simulate simple power supplies.
 
The Schottky diode "pcan" mentioned will fail serving in a FWCT setup that's fed by a 300-0-300 VRMS rectifier winding. :( This part will survive. :)

Sorry, but everything about the Amplion schematic screams CHEAP. For instance, the 6CA4/EZ81 can tolerate up to 47 μF. in the 1st filter position and the OEM used 16 μF. My guess is that the amp would have been used in a LOFI phonograph combined with a ceramic cartridge.
 
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Thanks pcan and Eli.
I've no doubt the schematic screams cheap because I suspect that is exactly what it was - but that doesn't mean it's not worth rebuilding and learning from, which is my intention.
My original post was intended to enquire whether anyone else had ever seen one of these amplifiers and find out a little more about Amplion.
It appears that made speakers (horn) back in the early days and a number of 'cheap' record player amplifiers. I doubt they even thought HiFi.

I've been rebuilding and repairing guitar amplifiers for 25 years or more now so have 'some' experience with the principles but surely bow to those who have the experience with the low distortion end of the market!

I'll post some pictures of the innards before and after...
Cheers,
Graham.
 
Here's a few photos of the innards.
As can be seen, the construction is pretty 'cheap' but it's been stripped and the chassis cleaned up a bit and now 50% through the rebuild.

The case is quite rusted but is responding to being cleaned up prior to a re-spray...

More pix later...
 

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