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RCA MI-9377 amps are here.

Ken Boyd

Ken Boyd

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As the header states I came across a pair of these a while back and had them on my watch list, price was reasonable, but I already have a ton of projects lined up for the next few years, but the seller made a major drop in price on them so typical me I purchased them.

I don't think these look very difficult to work on, the main filter caps have already been replaced by bypassing the old ones and putting new ones underneath. These are made to rack mount, so the tubes hang off the back, and the front panel is like the Altecs with a power switch, a meter, and a switch to check tube condition by clicking thru the selector to check each tube where if it is in the green zone, it is good.

I have most the tubes needed now other than a few rectifier tubes, so waiting on them. I measure the front edge with the amp sitting with the tubes up, like in the picture, and I think I have enough room to relocate the meter and the selector switch so it will be on the front edge. Then relocate the power switch, power cord, speaker binders, and RCA's will be on the back panel. I don't want a rack mount and get the water jet to make a bottom cover and add some feet. Well, that's the plan,

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Posted on a different thread about these 6L6 tubes, didn't want to hijack the other thread but these are them.

Made in German they all test good on my B & K which has been calibrated, but on my maxi matcher they test exactly as the seller claimed, at the bottom of the range. Which is ok by me as I usually run my amps at the bottom of the range to make the tubes last longer, and I can't hear a difference in all my amps.

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theyre not made in germany.
theyre made in china.

TAD is a german company that buys tubes from shuguang (mostly) and JJ. several variants are, according to TAD, proprietary. the tubes with the - STR (special tube request) suffix are proprietary variants.


Ken Boyd said:
Posted on a different thread about these 6L6 tubes, didn't want to hijack the other thread but these are them.

Made in German they all test good on my B & K which has been calibrated, but on my maxi matcher they test exactly as the seller claimed, at the bottom of the range. Which is ok by me as I usually run my amps at the bottom of the range to make the tubes last longer, and I can't hear a difference in all my amps.

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Did a little work today as it was a very nice day outside so I set up a table and a comify chair and did some rearranging on the amp. It now sits as a tabletop rather than a rack amp, meter hole cut holes drilled for the studs to hold the meter and mounted I also relocated the selector switch for the tubes on the left front both were tight squeezes as far as clearance but they worked out fine. Power switch I relocated to the rear, and I have yet to add the RCA and speaker binders to the rear they still come out of knockouts to a terminal strip inside. I am taking a break and will get the power supply hooked up and see if I have enough tubes to fire this baby up.


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Got to get my paint guys to get me a template made to paint the switch section positions on the front.
 
ceylon said:
theyre not made in germany.
theyre made in china.

TAD is a german company that buys tubes from shuguang (mostly) and JJ. several variants are, according to TAD, proprietary. those bear the suffix STR (special tube request) are such proprietary variants.
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Oh, I saw that German writing on the bottom and assumed it. Anyway they were dirt cheap so will give them a try,
 
Powered it up just temporarily on reduced power, everything seems to work but with a slight bit of hum which doesn't surprise me as it still has a lot of old caps and none of the resistors have been checked. These are old amps so I expected it, but the iron seems good as it sounds pretty good. I like that I was able to get the meter and switch relocated into the chassis and I like the way the layout looks on this amp. I am going to keep working out all the bugs on this one and then I will copy it on the other one and I think they will make a nice pair of music mono blocks.


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Are the power tubes triode strapped? If wired pentode or UL tbey would make decent output. Around 60 watts per amp maybe?
 
Unless the amp is wired in triode mode, right? I don't know anything about these amps and was just wondering if they were wired in triode mode, or pentode. Triode mode would be around the same output as only two 6L6's wired in pentode mode.
 
Selmerdave said:
I'm saying RCA sold them as 30W amps. They have regulated screens in pentode, not triode connected.
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Yes 30 watts per channel. Using these with my Altecs which is plenty of power to drive them well. Currently my only pair of 6SL7 tubes are in a pair of 845 mono blocks in storage, so I powered them up with some 6SN7's in that spot. I think when I put the right tubes I will get a little more out of the 6SL7's.
 
Lavane said:
Unless the amp is wired in triode mode, right? I don't know anything about these amps and was just wondering if they were wired in triode mode, or pentode. Triode mode would be around the same output as only two 6L6's wired in pentode mode.
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rca_mi9377a_sch (2).gif

This is the drawing of the amp here, as designed by the engineers at RCA. Would it be easy or feasible to change it to be Triode strap? I wouldn't mind having a drawing marked up that would use the existing parts to give it more potential.
 
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