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Post by vipertblck on Dec 25, 2018 4:08:31 GMT
picking up a 5 yr old restoration model c, but has MRA1-L6. thought this was odd as I read the c's came with MRA3 amps. anyway, the C is a good restored box. I have a model b as well with an MRA3-L6 in it, untouched, original caps. the model b plays, but is VERY quiet at max volume. im sure the amp needs to be rebuild to fix things and take away any danger/fire hazards. here's what I wanna try...
take the MRA1 out of the restored model c, and put it in the unrestored model b box just to verify it will make volume and all is well with the circuitry. if so, send out the MRA3 from the model b for a rebuild.
concerns; by doing this, do I risk hurting the rebuild MRA1 as everything else in the model B is "as-is" and not rebuilt or whatnot?
kevin |
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Post by Ron Rich on Dec 25, 2018 4:29:08 GMT
Kevin,
A MRA-3 will not work correctly in a model B phono, unless modified. The MRA-1 will work OK in either, unless it has had the AVC kit added. The only difference between a B and the later SAU type phonos, was the AVC was added to the amps., and an AVC switch was added to the mech. In order to use an AVC equipped amp in a B, the AVC must be shut off, or the B mech equipped with a switch. Ron Rich
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Post by vipertblck on Dec 25, 2018 4:50:02 GMT
ron,
I read a bit on this before, the AVC. if I remember and read correctly, on the MRA3 amp,to disable it you remove the 6SK7 tube, correct?
kevin
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Post by Ron Rich on Dec 25, 2018 14:31:30 GMT
Kevin,
You can, but I don't ! If using a MRA-3, in a model B, I usually add the squelch switch, to the mechanism, or if a customer insists on no AVC, ground pin three, of the mute plug. I "hate" anything with no AVC ( My "Direct TV, drives me crazy-er then normal, as the AVC is non-extant!).
Ron Rich
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Post by vipertblck on Dec 25, 2018 15:03:27 GMT
what exactly is this AVC?? I'm stumped with these box's as the B has an MRA3 in it, all original needs rebuild, and NO switch on the top of the mech, so how could the MRA3 have benefitted in this B w/o that switch?! Moving on the the second box, the C, has an MRA1 in it, which is worthless as the later mechanisms like this one in the C should have this switch on the mechanism already, and even if-it's not functional because the MRA1 has no AVC circuitry?
Do I have that all correct and understand it right?
Kevin
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Post by Ron Rich on Dec 25, 2018 15:18:39 GMT
Kevin,
AVC, also known as AGC, is the "automatic volume control / automatic gain control", which is intended to compensate for different recording volume levels between records-- ever watch the TV and all of a sudden, usually at the commercials, the volume soars, or is so low you can't hear it ?
That's a failure of the AVC--somewhere.
Other then the fact that the -1 and -3 use different final tubes, and the -3 had the AVC built in, both of these amps are virtually the same in all other respects. Seeburg offered an "optional AVC kit", for the -1's, sometime during production, or shortly thereafter (?). If a -3 ( or a -1, with the kit), is fitted to an A,B, BL, phono, lacking the squelch/AVC switch, AVC must be dis-abled, or you will get very low volume. HTH, Ron Rich
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Post by vipertblck on Dec 25, 2018 16:03:08 GMT
thanks ron,
excellent description! sounds like i'll have to take the rear board off to access behind the amp and receiver, and ground pin 3 on the mute plug in my B with the MRA3, and see if that increases the volume, as this box does not have the switch added on the mechanism that I can see.
kevin
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Post by vipertblck on Dec 25, 2018 16:30:27 GMT
looks like pin 3 in the mute socket goes to tube socket 6SL7-GT pin 1. the mute plug, as you said has no wire going to pin 3. this is in my B with the MRA3 amp. still necessary to ground pin 3 in the backside of the amp, even though there's no feed to if off the plug?
kevin
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Post by Ron Rich on Dec 25, 2018 19:34:27 GMT
Kevin,
Yep--this is what the added switch on the mech does !
Ron Rich
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