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Goodmans Maxamp 30

Fredrik 1977

Fredrik 1977

Super Member
i scored this unusual stereo at an auction.
His Masters Voice speakers with Goodmans 5" fullrange drivers. sounds pretty good for their size!

amp makes very little sound. needs a total restoration i think.
is it worth fixing it?

i have never seen this amp before, seems to be made in the mid/late 1960´s in england. some say it was Britains first transistor amp, but i´ll take that with a pinch of salt.

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well it turns out the amp is already recaped sort of

so i have a case of troubleshooting right here
symptoms are dead left channel very very faint sound on right, its distorted aswell and distortion increases with turning up the volume.

this is the opposite of a gullwing amp! :)
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not shure at this moment what that yellow ehm thing is
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well i think i found where the caps would go.
seems they thought it would be a good idea to throw the caps and solder the leads together.

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inductor said:
first amp to use silicon o\p transistors, 2n3055s if i remember, the yellow tape is to insulate the selector switch from the board, when working can sound quite good, the capacitors on the preamp at the top of the case usually need replacing too, as its a cap coupled o\p you should have dc on the speakers ?
Click to expand...

i didnt dare hook up speakers, just headphones.

all outputs are blown too

he probably blew his test speakers without the caps, wich took out the outputs.
 
closer investigation shows that the outputs are fine!
i installed some old caps out of the bin 2200/35V outputcaps from a pioneer SX-626.
still same symptoms so i have to tare in to this some.

obvious things i can see now is one broken trimmer on left board.
 
ok left amp can be adjusted for idle current 30mA the right amp wont respond its stuck at 13mA nomatter what.
the left amp cant adjust for center voltage, wont respond its just 0,7v
will replace the trimmers and see how it works.

also i pretty much need to recap it anyway since half of the caps used are of Chengx brand. other half is vishay BC.
 
HA! found it.
now both amps works but! only music in right channel. and when turning the bass knob some serious woofer movement is going on in both channels.
obviously i have to pull out the preamp.

oh and when play music its crazy high volume from the start on the knob.
 
recaped the preamp board it had some of those old blue philips axials, they where showing some 140ohm esr.

i put it back only to have the same problem, distorted sound on right and no sound on left,,,the scratching from pots is heard in both.

when i hook the cd directly to the ampboards i get crystal clear sound, so they work as they should i suppose.
 
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ok now i have replaced all transistors on the preamp pcb. kind of wish i hadnt:)
the symptoms are,
high distorted sound on righ ch.
very clear actually very good sound on left, BUT tone controls dont work on that ch.
very high dc thumps on right ch when activating either tapemonitor or mono button.
only tape monitor work as good as described above.
aux sound like cd is hooked up to phono.
 
been poking around in this mess some more, i think there are gremlins living in here!
cd in to tape results in clean sound on left, distorted on right, no tonecontrols on left but on right they work
cd into tuner results in almost clean sound on left, distorted on right, tonecontrols works on both ch....sort of:)
cd into aux results in ultra distortion in both channels, but tonecontrols work on both, also if i press tapemonitor in this mode i still hear right channel distorted only at a little lower volume.

i really miss my JAPANESE receivers:)


oh i forgot the right amp is acting up again, its stuck on 13mA idle current, i cant adjust it.
 
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so after replacing some old ITT zeners in preamp and replacing some already replaced transistors, and repairing a broken pcb track i missed the first times i pulled the extremely inacessible preamp pcb.
i get the following results
cd to tape perfect! on both ch
cd to tuner clear on left, faint and distorted on right
cd to aux ultra distortion and now also very dark,

replaced all transistors on right amp, still wont adjust.
 
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i see. would explain some of it. i cant see any broken cabling but there are a lot of cables in here!

i checked the diodes and they seems to work fine. they are 1N3754
 
Will replace the diodes when i get home. Suppose regular rectifier diodes Will suffice? Check wich preamp you have. Mine is the pa-8....the one in manual is pa-6 if i remember correctly

This turned out to be a recaped wreck! So far 2 zeners and 4transistors, and 1 trimmer + numerous caps were Broken. Outputcaps were missing. And it was recaped with questionable caps. Most Of it is now sorted out. Will try to get the bias adjustment to work next
 
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