Re: Info Needed: Silverstone Model 18801 Stereo (Tubes)
- From: Tim <tim@xxxxxxx>
- Date: Wed, 16 May 2007 12:50:53 -0300
In article <1179325969.559644.308250@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
sofie@xxxxxxxxxx says...
Tim:
This is a typical (of the era) hot chassis design that wired the
heaters in series to add up to 120 VAC.... if there were not enough
tubes to add up to the line voltage then a suitable high wattage
resistor was placed in series. The only isolation available was with
the speaker output transformer that isolated the speakers, speaker
jacks and terminals. Everything else was "hot", the input jacks, the
phono cartridge wiring and phono cartridge (probably a low quality
ceramic or crystal) and the metal shafts of the chassis mounted
switches and controls.... be very careful.
Are one of the channels working? If the tubes are lit, you should
get some kind of hum as long as you have rectified DC getting to the
plates of the 50EH5 tubes..... the red & blue wires on the speaker
ouutput transformer are from the Primary windings.... usually the red
wire goes to the B+... and the blue wire goes to the plate of the
output tube. You should have approximately 140 to 160 V DC at these
wires, assuming that the selenium or tube or whatever rectifier is
working and that there are no open resisitors, shorted capacitors (old
electrolytics are immediately suspect and if bad would cause tremedous
hum) or other faults causing the lack of B+.
This is not a complicated circuit and you should be able to figure
this out without a schematic.... many times a high out phono
cartridge could be connected directly to the grids (through a
resistor) of the 50EH5 and they could produce ample output without a
preamp tube.
50EH5
pin 1 Cathode & G3, usually connected to ground through a
resistor ... 150 ohm approx.
pins 2 & 5 G1 signal input
pins 3 & 4 heater (50V)
pin 6 G2, usually connected to B+ through a dropping
resistor, should measure at least 100 VDC
pin 7 Plate
Good luck and be careful with this hot chassis design.
electricitym
.
.
.
Well I do see a huge wirewound resistor bolted to the chassis near the
ac input, so that is probably is limiting the current to the heaters.
There is no sound from either channel. I tried my little signal injector
into pin 5 of the tubes, but got no output at all. If I inject the tone
into the 12ax7, I get a very faint tone out of the speakers.
I will check into the dc supply though, as it would take out both
channels if it was absent. I have found an old schematic from a
Fleetwood 50eh5 that looks similar to what I see in the chassis.
I guess I did not mention that I have the specs for the tube, so I know
the voltage range that should be present. My concern was that someone
had removed the transformer and hard wired the set to AC. The AC
Interlock was defeated, so I was a little suspicious that something else
may have been modified too.
This particular set seems to have a lot of extra components compared to
most other circuits of type I have found.
Thanks for the help,
- Tim -
.
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