Motorola EL84
- Thread starter tonyk
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primosounds
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Motorola is one of the few companies that have persisted from the beginnings of tube technology to now. they must have outstanding engineers to last so long. Replacing the various out of spec capacitors and resistors will no doubt give you a fine sounding amplifier.
tonyk
Super Member
tonyk
Super Member
Hmm, my Motorola knobs never gave me any problems. Maybe it's because they are pretty well flush to the surface.
I'm pretty careful when I pull them off though!
I cut myself while trying to clean that crud off, when soapy the knobs are hard to hold on to, one slight rotation of the knob between your fingers is all it takes.
Dandy, while we wait for Tony's impressions of the tone controls, I tried mine with and without. I prefer "without". The signal goes straight into the second triode, after which I installed a stereo volume pot right on the power amp's chassis. The signal just seems a little hotter, a little cleaner. Not very scientific, just my gut feel. This is for near-field listening through Tannoy Proto-Js. I like it a lot.
primosounds
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Wow talk about purple heart! Sacrificing some blood for your passion welcome to the club. This rates with throwing out my back when moving a HK Citation2 from the floor to the rack. Or getting an impromptu "geri curl" from touching the exposed metal of the hot cap in a voltage doubler circuit of a "rebuilt" (not mine) Fisher x202 amp.
Well Motorola is still around and i can refer you to a good lawyer friend of mine. He will accept partial payment in the way tubes.
primosounds
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I wanted to point out that the amp has no global feedback . Only local fb from the plate of the el84 to the plate of the 12ax7. I think i will try this circuit with some other transformers . I just got an amp in the mail that is SE from a Westinghouse console. Thank you for posting the schematic.
tonyk
Super Member
I gotta admit the main reason I used the volume/tone controls is I simply do not have the expertise to know how to to add a separate volume control.
I did breakdown and try this thing today without a recap. First on some test speakers, then with my Interface C's.
First off, it's dead nuts quiet. Not a lick of hum.
It has a very nice sound, to me it seems a bit more musical than my Arcam, with a smidge less bass.
Much to my surprise the controls are totally silent as well.
To your question Dandy about the tone controls, they work, though it doesn't seem like much happens around the flat portion of the control. But as you roll the knob well into the boost/roll off portion of their stroke it certainly adds or subtracts accordingly from the sound. It just doesn't seem quite as linear as what I'm used to.
I'm gonna reserve full judgement until this thing is recapped, but right now I like what I'm hearing, a lot.
primosounds
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In your case the tone controls work with V1 and V3. The components you need to worry about are c9 and c10 the coupling caps on the plate of the 12ax7. They go to the front of the tone and volume controls. The plate resistor and cathode resistor for each of these 12ax7 should be measure for tolerance, I usually change them out anyways.
Is this your first listen to a single ended amp? If you have sensitive or high efficiency speakers the sound from an SE amp can be quite beguiling. Those audio types who are only concerned about specifications, and i am not trying to step on any toes, don't know (or want to admit) how good an SE amp like yours can sound.
TomBig58
Super Member
Thread update: I am the proud new owner of the fruits of tonyk's labors on the EL84 amp. It isn't going to work for his needs. Considering the time and effort he put into the rebuild I kind of consider it "paying forward" that he moved it on to me. This is my first tube amp and it pretty much performed as expected but had a little more punch than I expected with it's low watt output. I coupled it with some 60's Nova 7's which are also new to me and an ipod with mp3 downloads. I'll get a little better feel for it's performance when I connect it to some of my other speakers of known quality and a cd player. I'm looking forward to playing with it and listening.
Thanks Tony and all you other AKers who helped him get it to this point.
Thanks Tony and all you other AKers who helped him get it to this point.
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primosounds
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How cool looking is that amp. I say all those chifi amps are missing the point of having something unique and more importantly great sounding.
A point to consider is that with so few components in the signal path everything has an effect on the sound. Of course, some things more than others. And rolling tubes is probably the easiest and most effective way to customize the sound to your liking.
These are great survivors of an era gone by...The amps make sweet sounding music. Neither the lowest lows or highest highs will have the highest fidelity, but sonically worthwhile for certain. I had a copper plated chassis stereo amp with passive controls, probably from a larger record player, which now resides with my daughter, sonny and granddaughters in their home. My son in law crafted a cool open top, painted wooden case, then mounted its' golden fascia plate in front. Functional and sounding sweet with corner mounted, small full range Philips speakers...
They plug their phones/digital files into a small hybrid headphone amp/preamp, then connected to the Moto and speakers, often for adorable "dance with the kiddies" listening sessions...
They plug their phones/digital files into a small hybrid headphone amp/preamp, then connected to the Moto and speakers, often for adorable "dance with the kiddies" listening sessions...
