I think I have tubes missing but I don't know what they are.

I just acquired a Lear Sigler brand, Bogen Communications Division, 30 watt, monaural audio amplifier, model 330A Series H-57, with tubes, that has 3 empty tube sockets. Unlike the other sockets which have the tube numbers on the chassis next to the sockets, these three don't.

I would like to give this amp away, and I think I first need to insert new tubes, but I don't know what to use. :)

The other 5 sockets are marked V1 6EU7 V2 6EU7 V3 7247 V4 7868 V5 7868

Since there is only one speaker output, the 2 pairs of matching tubes seems to me to indicate push-pull stages to the amp. Yes?

The other three sockets are labled X1, X2, and X3. I've never seen such names before. Perhaps this is a secret government amplifier?

The sockets are labeled Mic, Tape 1, and Tape 2. Each has a slide switch for Hi or Lo Impedance, on top of the open backed chassis.

Is it possible that a tube is needed for Lo impedance inputs and not needed for Hi impedance? Or is it vice versa?

I would like to be able to tell the next owner, if I can find someone who wants this, what tube he should use if he has the other impedance input. Does anyone want to wager a guess? The tube sockets are 9-pin and each has clips for a tube shield. Do they still sell tube shields? I have some, but I don't know if I can find them.

Four of the tubes are the original Bogen tubes, and the other, V3, the

7247, is a Telefunken tube labeled "Made in West Germany". So I guess this was repaired between 1945 and 1990. Can anyone suggest when it was made?

It also has little adjusting holes in the chassis for WMT-1 input and output, plus an RCA jack labeled "WMT-1 HIZ". Is that the same as High Z, and what would that be? :)

Any help is much appreciated.

If you are inclined to email me for some reason, remove NOPSAM :-)

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How very coincidental; I just repaired one of these and I will be photographing it from all angles and will post an url for the results (it is really a beautiful piece). Fortunately the schematic is easily found on the web but I will also include it on the site.

I was impressed that after years of operation, it sounds great, has no hum and very low noise.

Here is a tube placement diagram:


------------------------------------------ | | | V5 | | V3 V2 | | | | V1 | | V4 | | X3 X2 X1 | |-----------------------------------------

v1 6eu7 x1 t-200 input network v2 6eu7 x2 t-200 input network v3 7247 x3 t-200 input network v4 7868 v5 7868



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The 'X' sockets are most likely for microphone transformers. It was common in those days to supply plug-in transformers with 8 pin octal bases that looked exactly like octal tube sockets.


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I recall all sorts of things that used octal tube sockets. I had a couple old amps that had filter caps which plugged into octal sockets. Of course finding replacements became impossible. so I pulled the bases off dead octal tubes, removed the solder and soldered the newer and smaller caps on top. From waht I recall there were 3 caps in one.

Then the Ham radios often had plug in octal based coils to change the frequency, some real old circuits that used the old electromagnet speakers used octal sockets to connect the speaker to the chassis, which was both the audio signal and the electromagnet. Those magnet coils were often used a choke in the power supply. THey were also used on some PA systems that put out 70Volt speaker voltage and required individual transformers on each speaker. I seem to recall seeing a very old shortwave radio that used an octal for an antenna connector, and also recall an old car radio setup that used then for external amplifiers (way before our modern car boosters). I'm sure there were many more uses.

The OP said this amp has the 9 pin sockets for those X1 X2 X3. That's different because the octals had pins that things could be soldered to, whereas the 9 pins would be much harder to work with.

Either way, his amp might work just the way it is, since no tubes are missing.

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They actually helped heat the house in winter, which was a useful thing. The entire system contained around 40 tubes, including 12 6L6 outputs, and 6 5U4 rectifiers. I made wooden boxes for them, but had plexiglass panels so I could see the output plates glow. After several plexiglass panels warped from the heat, I put vents on the cases and small fans inside. In the summer on hot days, I would not turn it on. I'm sure the electric meter really spun.

The transformers were huge, with both the power and audio output transformers being the size of a 2lb coffee can each. I used to connect wave generators and would take it down to around 28cps, which felt like an earthquake. I had fun taking caps, diodes, and resistors of all different sizes and placing them across the tone generators to create all kinds of weird sounds. This was at a time when the synthesizer was something new, and I had a crude version made from all these oddsd and ends parts. A friend of mine had a Theramin too, and he brought that thing over several times. That was a fun toy to play with.

The biggest problem with this whole system is that the power levels would cause the turntable needle to bounce and skip around. That was mostly solved by putting the turntable in a wooden box with a tight fitting closed front door and placing foam rubber under both the turntable and the box it was in.

The other problem were all the noise complaints and police visits.

(I wish I still had all this stuff, and now that I live on a farm, I would not get noise complaints)....

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