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Interesting A-4 head [message #28432]

Tue, 01 February 2022 01:14

JDinPA17603
Messages: 69
Registered: May 2018
Location: Lancaster, PA

Member

Friend got an A4 amp the other day and wanted to know the values on some of the caps on the boards...wanted to replace the white mallory caps and a couple that were showing signs of cracking. So I had him get me his board numbers and send me a pic of the layout. Hmmm... no driver transformer. Board complement in the beast...
102 preamps (2)
302A/B reverb/tremolo/vibrato
402A/B Harmonic clipper/Selective boost
702 driver
502 plus 23 volt regulator
602 minus 23 volt regulator
When I checked the model number it says A4 but the serial number indicated it was built at the tail end of the A series and start of the B series.
Only issue is .47 volts DC across the speaker terminals and a slight amount of 120 hz hum.
He wants to change out the Mallory beasties and the filter caps to try and address the hum. The Mallory caps on the 702 are showing degradation along with the filters on the 502 and 602 regulator boards.
Mainly posted here in comments because of the odd board lineup.
If I need help with the DC offset I will open a post in Repair.
Have a great day, and it is good to see the board still up.

Old Us Navy Vietnam Vet
Playing for my own enjoyment and irritation of the neighbors.

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[Message index]

		Interesting A-4 head By: JDinPA17603 on Tue, 01 February 2022 01:14
		Re: Interesting A-4 head By: stevem on Tue, 01 February 2022 06:29
		Re: Interesting A-4 head By: JDinPA17603 on Tue, 01 February 2022 13:39
		Re: Interesting A-4 head By: stevem on Wed, 02 February 2022 07:19

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