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Info Needed: Silverstone Model 18801 Stereo (Tubes)

T

Tim

Jan 1, 1970
0
I am trying to get the old guy back up and running so I give it to
someone who has no stereo equipment, but wants to play some LPs. There
is no audio output at all, not even the usual hum. I did some research
on the output stage which uses the 50EH5 tubes. Most of the schematics I
have seen use an isolation transformer to power the tubes. This one does
not have a power transformer in it at all. All of tubes light up, and I
have checked them with my (don't laugh) Radio Shack Tube Tester. Most of
the tubes are fine, but 1 of the 50EH5 shows as gaseous and shorted. I
would like a schematic if possible, or some direction from anyone who
may recall how this company designed the stuff.

Another strange thing is that most of the schematics have the 2 50EH5
heaters wired in series with a high wattage resistor so they run off a
125 v ac or dc source. If I pull one of the tubes out of the chassis,
the other one stays lit.

I love working on this old stuff, but I need some guidance here. I
figured that if 1 of the tubes is bad, the other channel should be ok.

Thanks,

- Tim -
 
H

hr(bob) [email protected]

Jan 1, 1970
0
I am trying to get the old guy back up and running so I give it to
someone who has no stereo equipment, but wants to play some LPs. There
is no audio output at all, not even the usual hum. I did some research
on the output stage which uses the 50EH5 tubes. Most of the schematics I
have seen use an isolation transformer to power the tubes. This one does
not have a power transformer in it at all. All of tubes light up, and I
have checked them with my (don't laugh) Radio Shack Tube Tester. Most of
the tubes are fine, but 1 of the 50EH5 shows as gaseous and shorted. I
would like a schematic if possible, or some direction from anyone who
may recall how this company designed the stuff.

Another strange thing is that most of the schematics have the 2 50EH5
heaters wired in series with a high wattage resistor so they run off a
125 v ac or dc source. If I pull one of the tubes out of the chassis,
the other one stays lit.

I love working on this old stuff, but I need some guidance here. I
figured that if 1 of the tubes is bad, the other channel should be ok.

Thanks,

- Tim -

You don't say how many other tubes there are. There may be two
parallel strings of tubes. Do any of the tubes go out when you [pull
one of the 50 EH5's?


H. R. Hofmann
 
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
..
..
..
 
Hi!
There is no audio output at all, not even the usual hum.

You might wish to check the speaker system and its wiring. Sometimes
the voice coil in a speaker opens up, either because of abuse or
normal wear and tear.

If the speakers in this set are a conventional permanent magnet type,
you can disconnect the leads from them and use either an ohmmeter on
the resistance range OR a nine volt battery across the contacts of
each speaker. Clicking sounds or static from the speaker when you
connect the meter or battery indicate that it is good. Don't leave the
meter or battery connected for very long, or you may open the voice
coil.
This one does not have a power transformer in it at
all.

This is a so-called "line connected" or "series string" set. The tubes
are wired in series so their heater voltages will all add up to
roughly 110/120 volts. If the number of tubes and their voltages don't
add up to line voltage, then a large resistor may be used to drop the
voltage to the point where it is needed.

You might look into replacing this resistor (if your set has one) with
something more modern, such as a diode. This will make the set run
cooler and more efficiently.

Be VERY careful when working on this chassis under power. Better yet--
don't have the set on or plugged in when you're working on it. There
is absolutely no isolation from the power line and you could really
hurt or kill yourself by doing the wrong thing. If you want to test
the set while it is apart, plug it in, make sure the (hopefully
nonconductive) knobs are on, conduct your tests and then unplug the
set when you are done.
but 1 of the 50EH5 shows as gaseous and shorted.

Give this tube a visual inspection. You may be able to see the
"getter' inside it. This should normally be a silver color. If it has
turned milky white (or *maybe* red), the tube's vacuum is gone.
I love working on this old stuff, but I need some guidance
here. I figured that if 1 of the tubes is bad, the other
channel should be ok.

Maybe. It depends upon how the unit is designed. Chances are most of
the tubes are good. You will find the most problems with supporting
components, such as capacitors and resistors. The capacitors may be
left alone if they work, but for reliability (and possibly safety)
reasons you should replace them if it all possible. You should also
give thought to reworking the power system if it turns out that the
radio does in fact use a dropping resistor.

For more information, you might also try posting to:
rec.antiques.radio+phono

William
 
H

hr(bob) [email protected]

Jan 1, 1970
0
Hi!


You might wish to check the speaker system and its wiring. Sometimes
the voice coil in a speaker opens up, either because of abuse or
normal wear and tear.

If the speakers in this set are a conventional permanent magnet type,
you can disconnect the leads from them and use either an ohmmeter on
the resistance range OR a nine volt battery across the contacts of
each speaker. Clicking sounds or static from the speaker when you
connect the meter or battery indicate that it is good. Don't leave the
meter or battery connected for very long, or you may open the voice
coil.


This is a so-called "line connected" or "series string" set. The tubes
are wired in series so their heater voltages will all add up to
roughly 110/120 volts. If the number of tubes and their voltages don't
add up to line voltage, then a large resistor may be used to drop the
voltage to the point where it is needed.

You might look into replacing this resistor (if your set has one) with
something more modern, such as a diode. This will make the set run
cooler and more efficiently.

Be VERY careful when working on this chassis under power. Better yet--
don't have the set on or plugged in when you're working on it. There
is absolutely no isolation from the power line and you could really
hurt or kill yourself by doing the wrong thing. If you want to test
the set while it is apart, plug it in, make sure the (hopefully
nonconductive) knobs are on, conduct your tests and then unplug the
set when you are done.


Give this tube a visual inspection. You may be able to see the
"getter' inside it. This should normally be a silver color. If it has
turned milky white (or *maybe* red), the tube's vacuum is gone.


Maybe. It depends upon how the unit is designed. Chances are most of
the tubes are good. You will find the most problems with supporting
components, such as capacitors and resistors. The capacitors may be
left alone if they work, but for reliability (and possibly safety)
reasons you should replace them if it all possible. You should also
give thought to reworking the power system if it turns out that the
radio does in fact use a dropping resistor.

For more information, you might also try posting to:
rec.antiques.radio+phono

William

Several of the previous posters ignored the fact that the original
poster stated that when one of the tubes was removed, the other
filaments stayed lit This is not quite as simple as they believe.

H. R. Hofmann
 
T

Tim

Jan 1, 1970
0
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 -
 
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.

Ac interlock? I've never seen a valve radio or amp with an interlock
of any sort.

If putting signal on the op tube grids isnt giving you anything, it
should be simple to go round those op tubes and see if the voltages
are ok or not, and if not where not. And if they are, you know the
fault is somewhere between tubes and speakers.

There are a few problems with neutral chassis stuff (I'm presuming
this is single rectifier giving N chassis, not full wave rec giving a
live chassis as was popular in the 80s)
..
1. Plug it into the wrong socket and everything plugged into it will
be live.
2. Ditto if you get an electrical fault of some types
3. When handling the stuff plugged in, eg tape deck, cd etc, youre
connected direct to the mains, which isnt best practice.
4. Anything earthed plugged in connects N to E, and in some cases this
can melt wiring.

TBH I'd forget about giving it to someone. Interesting item maybe, but
is it really worth the risk.


NT
 
T

Tim

Jan 1, 1970
0
Ac interlock? I've never seen a valve radio or amp with an interlock
of any sort.

If putting signal on the op tube grids isnt giving you anything, it
should be simple to go round those op tubes and see if the voltages
are ok or not, and if not where not. And if they are, you know the
fault is somewhere between tubes and speakers.

There are a few problems with neutral chassis stuff (I'm presuming
this is single rectifier giving N chassis, not full wave rec giving a
live chassis as was popular in the 80s)
.
1. Plug it into the wrong socket and everything plugged into it will
be live.
2. Ditto if you get an electrical fault of some types
3. When handling the stuff plugged in, eg tape deck, cd etc, youre
connected direct to the mains, which isnt best practice.
4. Anything earthed plugged in connects N to E, and in some cases this
can melt wiring.

TBH I'd forget about giving it to someone. Interesting item maybe, but
is it really worth the risk.


NT
Yup it had one of those interlocks that were common on tv sets of the
same era. It was the kind that separated the ac power when you removed
the back. We all used to have cheater cords to work on the bench with
the back off.

I will be doing a more complete diagnosis of the tubes now that I have a
bit more info and know the dangers of the mission....

- Tim -
 
S

Sofie

Jan 1, 1970
0
hr(bob) [email protected] said:
Several of the previous posters ignored the fact that the original
poster stated that when one of the tubes was removed, the other
filaments stayed lit This is not quite as simple as they believe.

H. R. Hofmann

In your first reply post you mentioned that there could be 2 parallel heater
strings
connected to the AC line, which could be true....
that fact was not ignored but may be irrelevant..... even if one of the
tubes are bad,
some kind of hum or noise should be heard out of the other channel. The
best bet is
probably a B+ problem or open speakers??
 
I am trying to get the old guy back up and running so I give it to
someone who has no stereo equipment, but wants to play some LPs. There
is no audio output at all, not even the usual hum. I did some research
on the output stage which uses the 50EH5 tubes. Most of the schematics I
have seen use an isolation transformer to power the tubes. This one does
not have a power transformer in it at all. All of tubes light up, and I
have checked them with my (don't laugh) Radio Shack Tube Tester. Most of
the tubes are fine, but 1 of the 50EH5 shows as gaseous and shorted. I
would like a schematic if possible, or some direction from anyone who
may recall how this company designed the stuff.

Another strange thing is that most of the schematics have the 2 50EH5
heaters wired in series with a high wattage resistor so they run off a
125 v ac or dc source. If I pull one of the tubes out of the chassis,
the other one stays lit.

I love working on this old stuff, but I need some guidance here. I
figured that if 1 of the tubes is bad, the other channel should be ok.

Thanks,

- Tim -

Is it a "SIlverstone" or "Silvertone" The latter was the name Sears
Roebuck used for many of its products.

H. R. Hofmann
 
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 - - Hide quoted text -

- Show quoted text -

What is/are the total list of tubes. We need to see what the line-up
is, then we can start giving you much better advice.

H. R. Hofmann
 
T

Tim

Jan 1, 1970
0
What is/are the total list of tubes. We need to see what the line-up
is, then we can start giving you much better advice.

H. R. Hofmann
I have to put this project on hold for a bit. I have many, many things
on the go right now, and the person I was fixing it up for is not
interested in a tubed stereo system.

I did check the 50EH5 tubes voltages and they are way off, so I guess
the problem is somewhere in the power supply side. The chassis is a
jumble of wires and most of 'em are brown, so it makes it difficult to
trace the lines. I will fix it up though, just to add it to my list of
done deeds.

Oh, the 50EH5s *are* wired in series, with the rest of the tube
filaments off another line. When I pulled one out, the other one went
dark, but the rest of the tubes stayed lit.

- Tim -
 
Yup it had one of those interlocks that were common on tv sets of the
same era. It was the kind that separated the ac power when you removed
the back. We all used to have cheater cords to work on the bench with
the back off.

Was this US practice? I ask as I've never seen anything like that here
(UK)


NT
 
T

Tim

Jan 1, 1970
0
Was this US practice? I ask as I've never seen anything like that here
(UK)


NT
Well I'm in Canada, and it was very common until the 80's

- Tim -
 
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