Author Topic: 1964 Ambassador IV A-69 P  (Read 522 times)

Motorola Minion

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1964 Ambassador IV A-69 P
« on: September 27, 2018, 03:13:37 PM »
This was one of the hybrid models that is 85% tubes, with four output transistors for each channel. The 690 amp has the entire power supply for both tubes 300V and +/- 32 volts for the push-pull output transistors. I will recap the power supply first, before trying anything.

Before offering a reasonable sum at a well-known swap meet last Friday, I pulled all four fuses from the amp to confirm nothing bad went down. This amp is the type that direct-couples the push-pull output transistors to the speakers without a capacitor. From the schematic, it would seem a shorted transistor could fry the speakers. 

It definitely needs repairs to the legs before I can put it upright. The cabinet suffered through a few moves by the look of things. Fisher cabinets are one of the more damage prone, based on a lack of bracing found underneath. I have already used structural woodscrews to tie the rear legs into the base trim and glued one leg that split in half.
The legs and most of the "fruitwood" cabinet appear to be cherry, and like my 1964 Electra VII in "distressed walnut", will need to be stripped.

The amp and receiver chassis had all the 12AX7's swiped but the rare 6HU8 tubes were not ??? The Garrard type A record changer is complete and nothing else looks missing.

I was curious about the speakers first, so those are the photos below. Ill have to get a better picture of the tube map.
Tubes - Magical - Tubes

Dave

Bill

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Re: 1964 Ambassador IV A-69 P
« Reply #1 on: September 28, 2018, 09:20:18 AM »
This part looks good, can't wait to see the rest.

Bill

Motorola Minion

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Re: 1964 Ambassador IV A-69 P
« Reply #2 on: October 11, 2018, 10:45:40 AM »
I repaired and hardened all four legs, as this is a heavy one. The wonder of structural screws, polyurethane glue and impact drivers make the job easy. The photo below shows how the rear legs needed to be tied into the surrounding hardwood. All cherry where it counts but the veneer is not so great.

This may have been the age where price pressure of offering GOOD solid state made necessary some departures from good carpentry :-\
Tubes - Magical - Tubes

Dave