Davis Amplifier Model 105

1/26/2009 11:44:10 PMDave Froehlich

Hello All,
I'm working on a Davis Amplifier Model 105. Has anyone ever heard of this Brand or Amplifier? The tubes are 6CA5, A compactron amplifier tube (unknown type), and a 6EU7 pre-amp tube.

Thanks,

Dave

1/27/2009 12:15:00 AMDave Froehlich

Hello Again All,
The tube is a 7868. I don't have a schematic for this amplifier. But there's only one ceramic capacitor and a few resistors. Then there are 4 filter capacitors. Does anyone have a schematic using a 7868 amplifier? I'll see if I can find anything.

Thanks,

Dave
:Hello All,
: I'm working on a Davis Amplifier Model 105. Has anyone ever heard of this Brand or Amplifier? The tubes are 6CA5, A compactron amplifier tube (unknown type), and a 6EU7 pre-amp tube.
:
:Thanks,
:
:Dave

1/27/2009 12:53:20 AMWarren

Never have seen one before. Or knew of any.

But I guess there is ..

http://oldradioarchives.com/radio.php?radio=692

1/27/2009 10:14:36 AMDave Froehlich

Warren,
I didn't think to look there. I have the 105 but that one looks very similar. I don't have the top cover part.
Maybe someone has the schematic for the 105 or a schematic showing a single ended amplifier.
Thanks,

Dave
:Never have seen one before. Or knew of any.
:
:But I guess there is ..
:
:http://oldradioarchives.com/radio.php?radio=692

1/27/2009 12:10:01 PMEdd

With that tube lineup. . . .certainly seems that the unit might have been the last of the general purpose audio amps using

tubes, the novars clueing in on possibly in the early ‘70’s for its manufacture and it just might have been J.W.Davis in Dallas,

as its creator. They, have been into sound systems since 1933.

REF:

J.W. Davis Company Home Page

Certainly with this data, you can handle the situation, merely take on a mindset that you are working with an ‘ole amp

using a 6L6, 12AU7 and 6AU6, with the power supply typically being a silicon diode rectifier or a FWB unit.

REFERENCE DATA:

73's de Edd

1/27/2009 9:30:22 PMDave Froehlich(70414:70374)

Edd,
I made a mistake. It's a 6CA4. It looks like a rectifier. This seems to be a direct coupled amp. The only capacitors I see are in the power supply and there's a disc capacitor on the input. I'll check again. One of the ones in the can may be connected to the cathode of the output tube.

Dave
:
:
:
:With that tube lineup. . . .certainly seems that the unit might have been the last of the general purpose audio amps using
:
:tubes, the novars clueing in on possibly in the early ‘70’s for its manufacture and it just might have been J.W.Davis in Dallas,
:
:as its creator. They, have been into sound systems since 1933.
:
:REF:
:
:J.W. Davis Company Home Page
:
:
:
:Certainly with this data, you can handle the situation, merely take on a mindset that you are working with an ‘ole amp
:
:using a 6L6, 12AU7 and 6AU6, with the power supply typically being a silicon diode rectifier or a FWB unit.
:
:
:REFERENCE DATA:
:
:
:
:
:
:
:
:
:
:
:73's de Edd
:

:
:
:
:
:

1/28/2009 2:34:13 AMDave Froehlich(70421:70414)

Edd,
The 6EU7 socket is mounted to a small PC board. I had to resolder all the pins because all of them were loose. It looked as if almost no solder was used. Also,one of the ends of the B+ windings were connected to the 6CA4 wrong. It was connected to pin 6 instead of pin 7. Moving it made a big difference. It looked like it was a factory mistake. However maybe the Davis amp was a kit.
The power transformer has a single filament winding for all tubes including the rectifier. The filament winding has a center tap which appears to be connected to the input pin on the output tube. I'll check again. Is this correct? The amplifier seems to work ok.
I replaced all the electrolytic capacitors. I think I'm done with this restoration.
Thanks,
Dave

:Edd,
: I made a mistake. It's a 6CA4. It looks like a rectifier. This seems to be a direct coupled amp. The only capacitors I see are in the power supply and there's a disc capacitor on the input. I'll check again. One of the ones in the can may be connected to the cathode of the output tube.
:
:Dave
::
::
::
::With that tube lineup. . . .certainly seems that the unit might have been the last of the general purpose audio amps using
::
::tubes, the novars clueing in on possibly in the early ‘70’s for its manufacture and it just might have been J.W.Davis in Dallas,
::
::as its creator. They, have been into sound systems since 1933.
::
::REF:
::
::J.W. Davis Company Home Page
::
::
::
::Certainly with this data, you can handle the situation, merely take on a mindset that you are working with an ‘ole amp
::
::using a 6L6, 12AU7 and 6AU6, with the power supply typically being a silicon diode rectifier or a FWB unit.
::
::
::REFERENCE DATA:
::
::
::
::
::
::
::
::
::
::
::73's de Edd
::

::
::
::
::
::

1/29/2009 2:15:21 PMEdd(70482:70421)

Sir David:

Indeed, I was certainly wondering about your having given TWO different levels of power output tubes on that units typical single
ended output, but with my never having developed “off the top of the head” number familiarity with the very last generation of
Novar based power rectifier tubes,
mainly due to their limited final time of utilization, in the '70's. With them being used in low quantities, and nothing like the time period of ye olde 80, 5Y3 or 5-Useless-4 categories.

As per the PCB mounted 6EU7, I can also visualize the skimpy flow soldering action sometimes resultant from a low production run of boards, IF they didn’t have enough board run volume to” fine tune in”, the feed, speed and temp parameters of the board size and the solder wave baths “hump”.

Also, one of the ends of the B+ windings were connected to the 6CA4 wrong. It was connected to pin 6 instead of pin 7. Moving it
made a big difference. It looked like it was a factory mistake.

6CA4 DATA:

Unless there was something tied between the(ose) points,(pigtail fuses /low wattage current limiting, sacrificial resistors ??? ) that one leg wiring would certainly result in a half wave rectifier circuit instead of a full wave circuit.

However maybe the Davis amp was a kit.

I wouldn’t think so.

The power transformer has a single filament winding for all tubes including the rectifier.

Great shades of ye olden days 6X5 circuitry !

The filament winding has a center tap which appears to be connected to the input pin on the output tube.

Sounds like balancing out the phasing of the filament supply for any residual hum pickup, possibly even a hum balancing pot
could have been utilized for optimum nulling.

I'll check again. Is this correct?

I’m totally blind. . . .can’t touch and see the unit. . . you will have to fill me in on THOSE precise details.

73's de Edd

1/29/2009 10:00:57 PMDave Froehlich(70499:70482)

Edd,
Is there some way we could make a schematic out of this? There is still a tiny hum from the microphone preamp. There's no way to turn that part off when not using it. The 6EU7 is being used like (or is) a mixer. The mic and line have their own level controls. The mic jack takes a screw on plug and the jack center acts as a muting switch when there's no mic attached. Even so, there is a faint hum heard wihen the volume is turned all the way down. There is no adjustment. Is there something I can add to the mic pre-amp so that it's hum can be eliminated when not using it? Or do you think that the faint hum is coming from somewhere else?
The sound is very good though. I have the HV winding ends connected to pins 1 and 7 of the rectifier. The total voltage I measure on that winding is 525. So half of that is 262 AC and about 340 DC. That's not too high is it? It's the same voltage, but more noise if it's used half wave like it was. I have a tuner attached to it and it sounds great. The amplifer is connected like your example but the resistances are different. The capacitor on the cathode is 50 mf. I will give you all the values of the components later tonight or tomorrow. I think it would be fun to make our own schematic for it.
Thanks,
Dave

:
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:
:
:
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:Sir David:
:
:
:Indeed, I was certainly wondering about your having given TWO different levels of power output tubes on that units typical single
:ended output, but with my never having developed “off the top of the head” number familiarity with the very last generation of
: Novar based power rectifier tubes,
:mainly due to their limited final time of utilization, in the '70's. With them being used in low quantities, and nothing like the time period of ye olde 80, 5Y3 or 5-Useless-4 categories.
:
:
:
:As per the PCB mounted 6EU7, I can also visualize the skimpy flow soldering action sometimes resultant from a low production run of boards, IF they didn’t have enough board run volume to” fine tune in”, the feed, speed and temp parameters of the board size and the solder wave baths “hump”.
:
:
:
:
:Also, one of the ends of the B+ windings were connected to the 6CA4 wrong. It was connected to pin 6 instead of pin 7. Moving it
: made a big difference. It looked like it was a factory mistake.
:
:
:6CA4 DATA:
:
:
:
:
:Unless there was something tied between the(ose) points,(pigtail fuses /low wattage current limiting, sacrificial resistors ??? ) that one leg wiring would certainly result in a half wave rectifier circuit instead of a full wave circuit.
:
:
:
:However maybe the Davis amp was a kit.
:
:I wouldn’t think so.
:
:
:
:The power transformer has a single filament winding for all tubes including the rectifier.
:
:Great shades of ye olden days 6X5 circuitry !
:
:
:
:
:The filament winding has a center tap which appears to be connected to the input pin on the output tube.
:
:Sounds like balancing out the phasing of the filament supply for any residual hum pickup, possibly even a hum balancing pot
:could have been utilized for optimum nulling.
:
:
:
:I'll check again. Is this correct?
:
:I’m totally blind. . . .can’t touch and see the unit. . . you will have to fill me in on THOSE precise details.
:
:
:
:
:
:
:73's de Edd
:

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