restoring a 1934 Clough-Brengle mod OC RF gen

[Texasrocker]

I am currently restoring a vintage 1934 Clough-Brengle Mod O-C full-wave RF Gen. Its a 3-tuber ( tube lineup 1- #36 tube, 2- # 37 tubes) total 3-tubes filament AC consumption voltage 18.9 v ac total. This vintage pc of test gear is (missing) it's orig AC line-resistance "curtain-burner" AC cord. I need to rid lots!! of modern-day AC voltage for this ancient 3-tuber AC/DC test equip chassis. Anyone here ever restored one of these items? Any your vintage AC/DC chassis elec-resto tips would be highly appreciated, for best simple solution of dropping all this spare AC voltage, to insure safe AC only operation of this pc of vintage pc of test gear. Someone previously added a "outboard" small metal chassis with a huge vintage blue-colored ceramic power-resistor rated 260 ohms @ 30 watts. The added vintage resistor itself is "open", so I guess it didnt work out back wh
en the set was previously serviced many yrs ago.Someone added new filter caps subs, and the outboard huge power resistor previously, so Im also skepticle at best in restoring this vintage item. Simple math using Ohms Law again I figure?, but dissipating that much modern AC voltage is scary at best! Just thought I would ask here if anyone" seasoned techs" has ever restored a similar pc of 3-tube test gear before, and results? If you wish, you can see one of these vintage test-equip items here.
http://cloughbrengle.homestead.com/CBOC2.html

Any tips would be highly preciated!! I just bet this will be a very nice RF gen to add to my vintage test-equip collection, once fully restored? As with most of these type items, Im probably looking-past the simple solution of ridding todays incoming AC line voltage into the old cheap AC/DC test equip 3-tuber chassis? Im gettin old!!..but Im still tryin to save em if I can!! Any & All your suggestions would be very much appreciated!! The tube filaments & orig trans still check good!! Sign of hope anyways?? ol Tx

[rghines1]

Hi,

Got this spreadsheet long ago on the Internet that runs calculations for 3 scenarios. Resistor only, diode with resister, or AC capacitor in series with the filament string. Appears the best way to go would be using a 6.6 uF AC capacitor of at least 250V AC rating. Assuming 2.2 uF AC rated caps are available this should be feasible by putting 3 in parallel.

Richard

[Texasrocker]

Thanks Richard. Sure appreciate your help! I have the unit open on the bench, and am completely recapping it and adding all new point-to-point wiring. The old w.w. pots & toggle switches started working again after some tlc. I will try to locate the caps you suggested, to keep the heat buildup eliminated. Since I need to rid approx 102v ac ( from my modern day ac line) to the old 110 v pc of test gear, I did some quick math using ohms-law to calculate proper size dropping resistor.
Seems I need to use a approx 340 ohm resistor, rated at approx 36.3 watts to do the trick. Since I have a variac, I will bring the old unit up slow after restoration, and monitor amp draw, and do the old resistor heat-check by touch test.
I found 2 good - 700 ohm ea, 25 watt power resistors in my junk boxes. I will parallel them to get 50 watts, & approx 350 ohms, for test firing the unit. I figure they will get plenty-warm after awhile. I will most probably have to order the caps you suggested, on my next caps order, as my local supplier in my small city doesnt have these type caps.
If there is a chance I could get a copy of the spreadsheet-calculator online to download & print, I sure would appreciate the info (link) to find it on the internet and print it out.
Thanks again!!!

[rghines1]

Hi

Will need your email address to send as attachment, use PM if you like. Could not find it on the web anymore. Could not upload the spreadsheet to this forum because .xls files are not allowed. Did use a line voltage of 122 VAC in my calculation.

The resistors you plan on using are in good agreement with the spreadsheet's calculation. Good luck.

Richard

[Texasrocker]

Thanks much Richard!! I would be most greatful for your email of those spreadsheets!! Will PM you.
Sincerely, Tx.

[exray]

Tex, here's the page where that spreadsheet comes from. Or at least I suspect its the same one.

http://www.vintage-radio.com/repair-rest...calcs.html

There's some good reading there. Sort of helps with the logic going into the spreadsheet. I'd also be more prone to use the dropping capacitor just from a heat standpoint.

Digikey has a good selection of AC caps. Hard to find on their site so heres a link:
http://dkc3.digikey.com/PDF/T091/P1735.pdf

Don't see a 6.6 uf but maybe you can find some workarounds with an additional resistor, etc.

GL

[Texasrocker]

Thanks Very Much for all your help guys!! I will be ready to test-fire this old 34 mod Clough-Brengle RF gen in the next few days as spare-time allows. I found & printed-out info searching online, incl the orig schemat, & operators users guide. According to this info, this vintage test item was considered among 1st class back in the 1933-34 radio repair shops.
Specs: Clough-Brengle Mod OC RF gen.
* Range: 50kc- 30 mc
* all fundamentals without use of harmonics (6,000- 10 meters)
* Accuracy: 6-bands each covered by a dial 25" long in Dia, divided into 400 divisions, each division 1/16th inch wide. Readings to 1/10th accuracy. Each sealed tuning coil ( 6 in total), hand calibrated with crystal oscillators.
* Continuously variable in output, 1/2 mv to 2v. 400 cycle audio test note. External mod from from phonograph or beat-freq oscillator when desired. 110v AC or DC line operation without normal-variation of affecting overall operation.
* works for perfect alignment of any set
( as per the orig documents): Advances and changes in receiver design bring new probs for the serviceman. The methods and equip for testing and adjusting older sets are not suitable for todays new all-wave sets and for many of the recent sets employing entirely different intermediate freqs. Clough-Brengle Engineers have developed in the new Mod OC,a complete solution to the prob of testing & aligning all receivers, regardless of their reception bands or the intermediate freq employed.
Introducing countless entirely new electrical & mechanical features, its performance may be summed up as follows: The Mod OC provides every known intermediate freq ,broadcast,SW, on fundamental signals(no confusioning harmonics), at whatever signal-strength needed for perfect alignment of any stage, no matter how badly out-of-alignment or how great the amplification ,or high the sensitivity of the set.

Orig Price in 1934: List: $ 49.85 Net: $ 29.94

cant wait to bring this vintage item back to life, and check the accuracy with my digital freq-counter!
Thanks again for all your help Guys!! Muchly appreciated indeed!! ol Tx

,

[Arran]

I had a different model C.B about 15 years ago and the tube filaments ran from a transformer, just like every other signal generator that I have owned. Even the EICO, PACO, and Heathkit units had a transformer for the filaments, the B+ ran from the line. and those were more cheaply built then the C.B I had. From the information that I can find this device used to have a curtain burner line resistance cord, the operating instructions are here, it would be nice if they included a schematic.

http://novatech-instr.com/Fun/cb_1.pdf

Seems like a honky way of building a signal generator, just so they could sell to the 1% of the market that actually had DC line current. Hopefully this thing has some sort of isolation at the output end, it's a real shock hazard otherwise.
Best Regards
Arran

[Texasrocker]

Thanks Aaron! Thats the same website I downloaded my info from in regards to this vintage RF oscillator. I have many,many vintage RF gens here, and none are wired like this rascal! Ive already taken into consideration of the output shock hazard also. This particular unit had been seriously hacked before, and a very large vintage type ceramic power resistor added that previously- failed also,on the ac line to replace the orig resistance line cord.Orig tube fils still check good. I still have it on the bench, and will check for a orig missing filament trans! If one ever existed, I missed it! Thanks again!! Looks to me like this is a all-orig filament-string ac/dc type setup from the getgo. Since some info I read on this particular item "noted", never change the length of the orig curtain-burner ac cord, tells the full story? I may have missed a orig component, as all my other RF gens also have, like yours. In any case, Im ready to rid approx 103 v ac upon initial test-fire, heat dissipated into a 340 ohm 50 watt wirewound resistor for direct tube filament-string operation as a test. Im ordering some ac caps to use, if it belches good life again. That will help keep the heat in check. Thanks again for your help!! Im getting older, & my eyesight isnt as good as I wish these days for sure!

[Arran]

Yet another way you could go about it would be to have a look through the junk pile and see if you can come up with a transformer suitable for operating those filaments, something around the 20 volt range with enough amps. You could then add a silicon diode in series (or two) to drop it down.
Best Regards
Arran