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Stroboconn 6T tuner unit OPT?
Stroboconn 6T tuner unit OPT?
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Old 10th April 2018, 07:01 PM   #1
multi-volti is offline multi-volti  United States
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Default Stroboconn 6T tuner unit OPT?

I was just given half of a Stroboconn 6T mechanical instrument tuner.

The tuning unit half...the scanning unit with the motorized strobe discs is missing. I havenít looked closely enough yet to tell if the transformers have any ID #ís.

Found a manual online...

The Conn p/n for the tuning unit OPT is 56187.
It has a CT primary driven by parallel PO 6V6ís.
The secondary drives coils on a mechanically tunable tuning fork transducer...if itís like reverb tank technology...could be any impedance...whatever they needed.

Long shot question of the day:

Anyone know anything about this output transformer?

(Other than it being black and having steel & copper inside).

Thanks

Murray
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Old 10th April 2018, 11:11 PM   #2
multi-volti is offline multi-volti  United States
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I found a 1951 Radio-Electronics full text in archive.org that gives extensive tech. info on how it works, but nothing about the transformer.

I explained incorrectly above. Tuning fork is driven somehow by a regenerative oscillator PA with a pair of PP 6V6’s & output transformer. The extremely stable tuning fork oscillator then is amplified in the half I have with the PPP 6V6 quad. This power oscillator drives the motor that rotates 12 geared strobe discs and maybe the neon lamp that illuminates the discs. They run at different speeds in ratios as close to 2^(1/12) as can be done with gear tooth ratios. Each disc has multiple rings for higher octaves.

I have the Peterson Strobotuner app on my phone, the explanation of the mechanical version helps me understand what I haven’t gotten from the Peterson instrux (apparently I need more info to be less confused).

Only mention so far about motor on OPT secondary is the process of using a 500 ohm dummy load when the motor is not being driven.

That doesn't assure the motor is equivalent to a 500 ohm load but raises that potentially disappointing possibility...the OPT would not be suitable to drive a conventional loudspeaker if that’s the case.
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Last edited by multi-volti; 10th April 2018 at 11:13 PM. Reason: link
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Old 10th April 2018, 11:14 PM   #3
multi-volti is offline multi-volti  United States
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For anyone interested:

Full text of "Radio Electronics 1948-1992"

July 1951; search for Conn. There are 11 occurrences in there.

This link has 2 or 3 different vintage manuals, some with schematics.
Stroboconn
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Last edited by multi-volti; 10th April 2018 at 11:20 PM.
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Old 11th April 2018, 12:12 AM   #4
multi-volti is offline multi-volti  United States
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Ha - finding everything else...

https://patentimages.storage.googlea.../US2286030.pdf
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Old 11th April 2018, 03:36 AM   #5
PRR is offline PRR  United States
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Quote:
Originally Posted by multi-volti View Post
...That doesn't assure the motor is equivalent to a 500 ohm load....
Your later post has the info:
"The motor was made by Bodine Electric Company, Chicago. (It's rated at 110 V, 55 Hz. 0.26 A, 1/120 HP. 1-phase, continuous duty, 1650 RPM. Capacitor 3.75 [ĶF?], 40 įC temperature rise, No. 7270733, Type NYC-12.)"

110V 0.26A is 423 Ohms 28.6 Watts. (So you see why two 14W pairs of 6V6.)

Note also that the amp ran "ONLY" 55 cycles (Hz). There's a trim with fork weights but this will be slim. So far you only can expect say 50-60Hz frequency response. In fact you can't wind an untuned transformer that narrow, but such iron will sometimes cut-off by 500Hz. (And unlikely to go far below 50Hz because it was already heavy/costly.)

The only thing really comes to mind IS a motor. There is sometimes need to drive small sync motors away from 60Hz. Such as turntables for "78"s which were often not cut at 78. Or the home-cut disks I got with a portable disk-cutter, some recorded on bad power. Build a small 30Hz-200Hz oscillator and let the Conn amp drive the turntable motor. However for many years it has been so much simpler to transcribe at whatever speed and re-speed it digitally.
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Old 11th April 2018, 08:30 AM   #6
Enzo is offline Enzo  United States
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I still have several Conn 6T5 12-wheel tuners. One working even.

The neon is simply driven by the mic circuit. It flashes at whatever frequency you feed the thing. The wheels all spin at a steady rate, their motor driven by the power oscillator.

The fork system is extremely stable. But it is mechanically tunable. The big dial on front will adjust the tuning 50 cents either direction.

The motor spins steadily, and the gears spin each strobe disc at a particular speed. The light from the mic amp will then sync in with whatever disc is spinning the right speed.

The transformer is driven push pull with 6V6s, but it is still basically a fancy power transformer. Since you lack the scanner, I won't go into servicing it.

The transformer won't be an off the shelf item.
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Old 11th April 2018, 04:03 PM   #7
multi-volti is offline multi-volti  United States
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Thanks, PRR & Enzo.
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Old 13th April 2018, 08:53 PM   #8
multi-volti is offline multi-volti  United States
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Default Stroboconn tubing unit PPP 6V6 plate & grid connection questions

I donít have a direct schematic link yet, which Iíll try to do this weekend, which seems preferable to sending people to a complete PDF manual elsewhere with a Ďsee page 14í instruction.

But this seems simple, so Iíll try describing. Itís the tuning unit of the Stroboconn, an AC source to drive the synchronous motor in the other chassis with the strobe dials.

Two push-pull pairs of 6V6GTA, B+ From 5U4GB (350 VDC) to CT of OPT thru a 100 ohm resistor (no UL taps).

One of the upper tubes and one of the lower tubes each have plate connected directly to Ďendsí of OPT primary (325 VDC). Each parallel pair has a 47 ohm resistor between the plates (one is connected directly to the OPT, the other through the 47 ohm resistor).

The upper and lower pairs both have a 470 ohm resistor between their (control) grids. (One resistor per pair). Possibly a shared grid stopper. Two tubes have their grids capacitor coupled to the plates of a 6SN7GT phase splitter that each have 82k plate resistors fed from the 290 VDC (B+#2?, same source as 6V6 acreens).

All four 6V6GTAís have screens connected together (290 VDC) to a common 4k dropping/decoupling resistor that goes to the 5U4GB (same 350 VDC the 100 ohm plate decoupling resistor is fed by).

All 4 cathodes are connected together and share a common cathode resistor of 125 ohms (unbypassed) to a common ground point. 19 VDC at cathodes per schematic.

The control grids have a little more complex compound connection I should leave for a schematic graphic. They are not symmetrical. The lower pair have a 150k grid leak resistor to ground, but the upper pairís 150k grid resistor goes to a 10k resistor (160k to ground). The upper and lower tube that have no grid stopper before the coupling capacitor.

The 10k between ground and the 150k upper grid leak resistor goes to the Ďlowerí 6SN7GT phade splitter grid. Uh-oh, some kind of feedback?

There is no adjustment or measurement option to balance the cathode currents.

The questions (if this is a vivid and accurate enough description):

Do the 47 ohm Ďseriesí resistors in one plate circuit Ďbalanceí the current in each parallel pair like emitter resistors in parallel BJTís? (I should use the analogy of separate cathode resistors, but something is holding me back).

Does anyone else think the grid stopper arrangement is marginal?

What I do know is that the signal level is uniform, other than aging, etc. in other words itís set up and only adjusted perhaps in a calibration step.

Iíll figure out a way to link to a schematic image when I get home.

Thanks for reading, if not looking.
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Old 13th April 2018, 11:40 PM   #9
multi-volti is offline multi-volti  United States
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Default Tuning Unit amplifier

Stroboconn 6T5 Tuning Unit amplifier - Google Photos

Of course I am going to make some changes, but want to study/learn from the things I haven't seen before.
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Last edited by multi-volti; 13th April 2018 at 11:49 PM.
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Old 14th April 2018, 01:37 AM   #10
multi-volti is offline multi-volti  United States
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Looks like Thordarson 32W10 had similar 10k ‘asymmetry’ with two high value (470k?) resistors in a 6SL7 circuit similar to the 6SN7 one I described.

I guess I just haven’t seen enough variety.
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