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Old 8th May 2009, 2:44 pm   #121
stonehopper
Retired Dormant Member
 
Join Date: Apr 2009
Location: St Albans
Posts: 50
Default Re: Roberts RT7 - problem

The AC128's have a TO-5 layout of 'pin out' as shown in http://www.vintageradio.me.uk/info/germanium.htm#cases. The OC81M's I had suspected, as was conformed by another poster, as having a grey line on the jacket in place of the paint mark against the collector pin. I still think this may have been correct, and believe I did the install in the correct order.

However, I have contacted Cricklewood for confirmation of the 'pin out' on the AC128, and as both Tim and Graham have stated, the metal tag protrudes nearest the emitter.

Prior to testing, battery Voltage at 9.6V
Results of checks:
Bias:
Followed instructions exactly, with TR6 & TR7 NOT installed, meter set to 0 - 20V DC Red lead to chassis and black to junction of R26 & R27 = 0.2V

Voltage check on TR5;
Actual/Service sheet
Base: 1.87V/1.69V
Collector: 9.15V/8.7V
Emitter: 1.75V/1.6V

Current:
Meter set at 20mA range (3 o'clock on my meter) = 0.00
Meter set at 10ADC (with plug moved to correct socket) = 0.01
(The latter being about the same as current passed through my body between fingers held on probes).

After testing, battery Voltage = 9.48V.

How are we doing?
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