Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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

mm wrote:

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.


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:

FRONT
------------------------------------------
| |
| 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

Regards,

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


"mm" wrote in message
...
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?

snip

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.

Dave

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

On Jan 31, 1:29*am, wrote:
On Thu, 31 Jan 2008 00:29:02 -0500, mm
wrote:





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 *:-)


This is the kind of thing I'd love to play with. *I still love the old
tube amplifiers. *When I was in my 20's I was bound and determined to
break the sound barrier with tube amps. *I came close when I put
together 3 separate amps, using four 6L6 outputs in each amp, and ran
them to their power limit. *Then I designed a stereo output that
powered the 3rd amp with a combined left and right channel run through
an old spring reverb, and had instant surround sound before such a
thing existed. *Using multiple guitar 15" 12" and 8" speakers, plus
horns, in cabinets as large as most home refrigerators, I came close
to breaking the sound barrier, when I blew out the living room window
in my apartment and really ****ed off our landlord who lived below us.
Of course this was the 60's and when he came up bitchin', a few beers
and some other stuff that I cant mention, got him pretty mellow and he
spent the rest of that night listing to our own private rock concert,
and a piece of cardboard tacked over the window. *It still amazes me
that our redneck neighbor did not call the cops with a noise
complaint, because he was always hassling us, and we were missing a
window facing his house. *We figured he must have been drunk that
night.

Anyhow, I still love tube amps. *They bring back good memories, and
they had a warm sound that no semiconductor amp will ever have.
Getting feedback thru the tubes themselves was a something desirable
for my impaired state of mind at that time.... lol

Anyhow, enough reminising....

Here's your tubes.

*V1 6EU7
*V2 6EU7
Preamp Tube. probably one for each tap input.

*V3 7247
Preamp Tube, probably for the mic input. *Also known as 12DW7.

*V4 7868
*V5 7868
Push-pull outputs. *Note they go to the output transformer.

Your rectifier is likely solid state diodes.

This should be all you need for a mono amp to function.

I'm sure you can still get the shields, but old tv sets are another
source, or you could actually make them from tin cans, or pieces of
pipe. *

WMT-1 HIZ is probably HI Impedience.

As far as those tube sockets, I originally would have guessed them to
be inputs for your three input types. *Back then, they did odd things
like that. *But the shields throw me off. *So, I guess I am not really
sure.....

I did some googling. *I found this:

A interesting discussion, where someone says this:
The M330 is in Sams Photofact folder 497-4, but 330A isn't covered. I
have the folder for the L330, which uses 6AV5 output tubes - don't
think it's very close, but email if you'd like a scan -
tbavis(at)rochester(dot)rr(dot)com.
Here's the web link. *Email that guy !!!!http://www.diyaudio.com/forums/showthread/t-112347.html

You can buy the manual here, for $25http://www.tech-wiz.com/store/view_product.php?product=M330A

If you got a dig. camera, take some pics and post them on one of the
binary newsgroups or a website. *Both pics of the top side of chassis,
and the under side. *I could likely tell you more if I saw some pics
of the circuit, if they were on the large side so I can clearly see
the parts.- Hide quoted text -

- Show quoted text -


Not only did the tube amps give you warm sound, from your line-up they
also gave you a warm feeling and spun the electric meter pretty fast.
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