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Cool 15 watt PP with el84 + ef86s

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  • Cool 15 watt PP with el84 + ef86s

    I just picked up a handsome 15 watt push pull PA amp made in Vancouver in the 60s by Barvic Engineering Ltd. It has a pair of EL 84 power tubes and a 12ax7 for a phase inverter. The recto is a 6ca4 tube. The preamp has a pair of ef86s which is unusual in north america and also a 12 au7 in the preamp circuit. There are two input jacks on the front, an rca phono input on the back and a 1/4 inch jack on the top that is connected to the choke. It has a feedback loop so I'm assuming it runs in Class AB. All I have done to it thius far is relace the power cord with a grounded one and removed the death cap. I also put some nice chickenheads on the front. The transformers as well as everything else on this amp look new. It's a bit cramped in there but I think it would make a killer little AC15 or 18watt Marshall clone.
    I'm drawing out a schematic of sorts by hand and am a bit befuddled by the input jack on top that connects to the blue, yellow and black wires of the choke. The fourth lead on the jack connects to the on/off volume pot and also to a terminal strip which ties it to the cathode? an ef86 pentode. This ef86 pentode has a short piece of wire connecting the cathode to the anode from the pinout diagram I have. I haven't plugged a guitar into this jack and want to know what it's for. This amp has a hum cancelling device as well. Also, The volume pot works only as an on/off switch when plugged into the input jacks on the front it just hums if you turn this pot up. The mic volume works fine. This will be my first build and think it's a fairly good amp to start with. It sounds extremely bassy but sounds not too bad with the bass rolled way back and the volumeClick image for larger version

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    Any input would be swell!

  • #2
    more picsClick image for larger version

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    • #3
      It looks really cool and the tube complement is cool- but how does it sound?

      If it's too bassy then maybe some smaller coupling caps or smaller cathode bypass caps are in order.

      jamie

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      • #4
        Looks like you got a good find there !
        the input jack on top that connects to the blue, yellow and black wires of the choke
        I suspect that this is not a choke but a mic matching transformer to allow for low impedance mics.
        The jack looks like a TRS type which fits with the above ie a 3 wire circuit -balanced low impedance input.
        Alternately it may be some kind of line out independent of the volume control.
        The picture doesn't show the numbers on the mystery transformer perhaps 'oogling them will
        help to identify it.
        Double check the pins it connects to - does seem a bit odd.
        I wouldn't plug anything into it until I'd figured out what it was.
        I gather from another forum that they also made amps suitable for speaker line distribution where multiple
        speakers could be connected each with its own transformer (70v/100v line).
        As this transformer connects to the input side I doubt its for spkr line distribution.

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        • #5
          I must confess to being a total noob here. I totally appreciate your input and advice. I am fortunately a very fast learner if it's something that I am interested in. The "choke" I am referring to has the big cast iron round cap on top and has "Barvic" cast into the design on top. This must have been something the company thought was worth manufacturing. Barvic was a small company that made PAs in vancouver back in the 50s and 60s and made very few of them as far as I can tell. Next to nothing is available online about them. I just assumed this was a choke. Also, why would you need 3 preamp tubes in such a small simple PP amp? One EF86 could easily push enough juice to the power amp. But two EF86 pentodes AND a 12ay7 triode seems like something I need to learn more about. The power tranny has 44176 stamped onto it. The OT has nada.

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          • #6
            The Jack on top is a mic input for a separate channel. This amp as it is has kind of a Gomer Pyle voice to it. You know how Randy Travis and some country singers sing like theres stuff caught in their throat. It's the Gomer Pyle voice. Sounds good for Jazz. The amp is really touch sensitive to how you play. Pick attack makes a huge difference on this.

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            • #7
              Just a guess, but the shape of bell covers on the PT look a lot like those on an early Traynor I have .Traynor used Hammonds and it seems likely yours might too being as the are both of Canadian provenance.
              SG

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              • #8
                I just peeked at the old DB2E Hammond PT on my 1972 Traynor YGL3A and they look identical other than the size and paint colour. The bolts that hold the bell covers are phillips on the PA and flatheads on the Traynor. Most Canadian stuff from the 1950s onward uses Robertson(square head). You can identify a lot of Canadian made products by the Robertson head screws and bolts.

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