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Author Topic: what to do with this?? I need a handwheel for this tank  (Read 10153 times)
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Patrick J. / KD5OEI
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« on: August 06, 2013, 09:50:37 PM »

always more stuff. The small bottle is a 6L6G. The tank is from a GPT-10. Had not imagined a bandswitching coil with a 1/2" shaft worm drive. I could not tell from the manuals how this was mechanically operated. Somewhere there's got to be a big knob..

There was a wish to build up a 3CX3000 unit with one of those multiband tanks al la MB-150 but a bit larger. But this may do instead, even be some overkill.

time to buy a gallon of tarn-x or brasso, something.. soap first.


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Radio Candelstein
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« Reply #1 on: August 06, 2013, 11:49:50 PM »

Geez Louise I think you'll need more than a hand crank maybe a PTO drive Cool what's the weight of that thing?

Dave
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« Reply #2 on: August 07, 2013, 12:32:09 AM »

surprisingly light, maybe 10-15 lbs. The base is aluminum. It's mostly air and tubing.

It apparently turns round and round, maybe a reduction motor was used in the TX originally. I did not see any provision for position detection.

It's not easily turned, but I am sure it needs a complete cleaning and relube. There are bearings to consider, probably gummed up.
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Radio Candelstein
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WTF-OVER in 7 land Dennis
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« Reply #3 on: August 07, 2013, 02:23:21 AM »

eBay # 400495357091

Cheap for a man-sized macho knob Cool.

73DG


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« Reply #4 on: August 07, 2013, 10:42:55 AM »

eBay # 400495357091

Cheap for a man-sized macho knob Cool.

73DG
Just what  Captain Neemo used in 20,000 leagues under the sea.
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Fred KC4MOP
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« Reply #5 on: August 07, 2013, 12:19:04 PM »

That coil has a fist sized knob with a geared right angle drive as it is used originally in the GPT-10K.
The coil does not have quite enuf inductance for 160 meters..You will have  to add a little extra to it to get the transmitter on 1885kcs....
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W3RSW
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Rick & "Roosevelt"


« Reply #6 on: August 07, 2013, 01:54:05 PM »

Something doesn't "latch" for me.
That worm drive spur wheel is made of what looks like brass, hence can't take a lot of torque or abuse over time.  This tells me it didn't have much load in ordinary service.  So why the worm for a simple switch?

 How do you "feel" an index or stop at each band position?  A many turn hand wheel via the worm will make it turn easier but how is the tap position indicated?

It obviously is a simple tapped coil, switched taps only, not continuously variable inductance that a nice hand wheel and vernier, worm drive would call for so why not get rid of the box, worm drive assembly and mount a simple, large bar type knob?  Is there an index?

How did the GPT-10K show when to stop the worm?  Turns counter?
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RICK  *W3RSW*
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« Reply #7 on: August 07, 2013, 02:41:49 PM »

GPT-10K manual:
http://www.virhistory.com/tmc/tmc_pages/tmc_manuals/manuals_db/gpt-10k/tm_gpt-10k_volII_nodate.pdf
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w1vtp
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« Reply #8 on: August 07, 2013, 06:56:15 PM »

I like your link coupling coil form.  Never heard of Seagrams in the RF inductor product line business.  Wonder what else they make

 Grin
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« Reply #9 on: August 07, 2013, 07:44:51 PM »

I like your link coupling coil form.

Are you sure it isn't part of a still? Cool

73DG
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Rick & "Roosevelt"


« Reply #10 on: August 07, 2013, 07:47:33 PM »

Ok, W3VW I got 19 pages of manual, mostly addendum and parts list.

Only reference to final tank was:
L245 part no. CL143, IPA RF tank 12-28mc
L246 part no. CL174, IPA RF tank single layer wound 23 turns.

Must be not downloading rest of manual with pix, etc.
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RICK  *W3RSW*
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« Reply #11 on: August 07, 2013, 08:59:58 PM »

That may be the wrong manual section. IPA V203 is a PL172 or something some 1KW output tube. It has its own pi network.  The 900-series of component reference designations are for the PA section.

I d/l all the manuals I could find. none show the mech arrangement, but there is that fist size knob, and above it a window indicating each tuning range of the selected band. Som perhaps the knob is turned a few times, and by some equivalent gear ratio, the dial rotates to be fully centered when the switch is in the right place. That's speculation.

There are no detents, no way to feel the places. Possibly a separate switch was connected to the indicating dial to tell the set what band it was on.

Getting rid of the worm is possible, but the torque for turning is rather high because of the contact type and the pressure is substantial. A 6" handwheel sans worm would still be hard to turn against the contact friction.


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Radio Candelstein
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« Reply #12 on: August 07, 2013, 09:02:37 PM »

GPT-10K power amplifier rf deck pics and schematic.
No 4CX5000 for me, too fussy, does not like mistakes with GG service, as the grids are small, and in AB1 it explodes everything if it runs away due to all the gain.. Maybe a GG or grid driven 3CX3000 is best.
The pictures tell me the worm shaft has been cut, too. see it looks very long in the book picture. It also goes into some kind of bracket-deal.

ok, so the tank is L903, with the 1.5 turn being L902. (L902, the smaller 0.5 turn section, or indeed any 1-turn coil, makes me think of 6 meters..)
Loading is C928,
Tuning is C927.
Fil choke there, L915.
In this schematic it was modified (as part of GPT-40K), normally C927 is a 25-700pF unit and C928 is 50-2000pF.

The chokes L906, L911, L914 are plate chokes.

C930 is unusual in that it decouples the lower ends of both the tune and load caps.
I don't understand why this was done as it would seem to affect tuning and loading a lot and makes those tune and load caps 'smaller'.
Any explanations for that unusual part of the original circuit?


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Radio Candelstein
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« Reply #13 on: August 07, 2013, 09:22:05 PM »

here is the right schematic. sorry about the other one.


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Radio Candelstein
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« Reply #14 on: August 08, 2013, 10:25:26 AM »

What is the value of L-914?  ...or what is its inductance ratio compared to L906?
Are the "45's" inductance in uh?  If so, sounds too little, but maybe they are, hence 1:1 ratio.

Looks like a circuit similar to what Alpha (ETO) has done in the Model 89.
L906 can't decouple RF over the whole range, particularly the upper freq's without toasting so 'halfway' up the coil in one model or using split coils in another, a bypass cap. to ground was placed by Alpha to help upper freq. decoupling.  In the case of the Alpha, a certain band of WARC freqs caused the toasting.  Alpha's two coil ratio seems to be about a 1:1.5 ratio.   Alpha's add'l bypass cap is switched in via a HV relay at the upper freq's only.

Concerning C930, your right. It effectively in series to ground for RF with C-tune and C-load allows finer control (or any) of upper freq's.  Perhaps because of C-GP in the 4cx-5000, C930 allows better efficiency at the upper freqs.

Another thought, since C928 and C930 are voltage dividers, this allows C927(tune) to partially bypass the whole RF final coils' inductance chain in the Pi Net at specific freq's determined by at least two of the B+ RF chokes.  Be interesting to Kirchhoff that baby via mesh and node!  What would Thevenin say?  Grin

Was this a mod or always in original?  
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RICK  *W3RSW*
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« Reply #15 on: August 08, 2013, 10:32:27 PM »

L914 is 38uH. the numbers are the values for all.

This last one is the original, book circuit, for the GPT-10K to standalone as a transmitter to a 70 Ohm line.
(as opposed to being a driver for the GPT-40K stage).

I believe L907, 912, and 913, and C916, are out of the picture when running to a coaxial cable.

A simulation would be interesting, beyond what I understand to set that up and probably beyond the free tools, weird circuit.

The breaking up of an RFC for different frequency ranges to avoid resonances has been discussed. This thing is continuous tuning. Maybe the elements achieve that in the circuit?

Could C930 serve to keep the circulating current through L902 L903 C928 C927 away from ground or somehow isolated to itself?
What I mean is there is a square or maybe bridge-like thing made of L902 L903 C928 C927, and the tube is at the junction of L902-C927, and the output is at the opposite "corner", the junction of L903 and C928.
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Radio Candelstein
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