EB5AGV's C-line repair notes

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Drake C-line Drake C-line

These are articles about my Drake C-line, posted in the Drake mailing list.


Date: Mon, 03 Nov 1997 18:56:49 +0100
From: JOSE V. GAVILA (EB5AGV/EC5AAU)
Subject: Modified R-4C: HELP, please!

Hi Drake gang,

Well, I've just received, after a 2 month trip (sloooow boat mail... At least, it is cheap :-) !), a nice R-4C, S/N 27813, with _lots_ of modifications.

I was aware of some of the mods:

(1)Sartori SSB Audio Low Pass Filter
(2)Sherwood LM383 Audio Amp
(3)3rd Mixer Injection Signal Mods
(4)Power Supply hash reduction
(5)AGC mod (Klinman, March 1980 CQ)

But once opened (the first thing I do always to the equipment after a long trip and also to satisfy my curiosity ;-) ), I've found other mods. Some of them are, as the other 5 previously listed, documented at the end of the (original) manual, with a copy of the corresponding articles / documents:

(6)TL422 Product Detector
(7)Power Supply mod (Klinman, February 1982 CQ)

And other mods completely undocumented:

(8)Sherwood Engineering filter model CF-600/6 (located where the standard IF filter should be).
(9)Sherwood Engineering filter model CF-6K/8 (located in the aluminum plate which supports the variable IF coils, with double sided adhesive tape).
(10)Relay (multiple contacts): I suposse it selects from one of the above filters, depending on the mode.
(11)(not exactly a mod) Extra Crystals: 39.1, 40.1, 39.4, 35.6, 29.1, 26.1, 21.1, 12.6 MHz.

There are perhaps more mods I'm still not aware of...

This unit came WITHOUT optional filters nor NB (although I have already a 250Hz and a NB-4 in the mail to my home), but with the original manual and box.

What I would like to get is information about these mods; which ones are keepers and which ones I should remove. Also, any experience with any of the mods would also be welcomed!.

And, as a final thing, I would like to get an estimate of what this receiver is worth AS IS... I _think_ I made a good buying, but...

Thanks a lot!

Best regards.

JOSE


Date: Sun, 09 Nov 1997 21:37:09 +0100
From: JOSE V. GAVILA (EB5AGV/EC5AAU)
Subject: Help: T-4XC no power output

Hi Drake gang,

Some days ago I commented about a R-4C I had just received. Thanks a lot for all your help with it; I have it working and it is really a hot receiver in SSB (I need a CW filter to check it in CW, but as it has the 600Hz Sherwood IF filter, it should be also good there!).

Well, last friday I received its companion, a 9+ looking T-4XC, in its original carton, with its manual and some spare tubes (2 x 6JB6 :-) , 2 x 12AX7A, 12BY7A, 2 x 6AU6A, 12BA6). Only thing I already knew about this unit was that it had a _very_ low output. I have checked it and, really, output is NIL!. To check it (as I'm completely new to T-4s), first I followed the manual procedure to check the bias. I could get it in 0.07A plate current without trouble, soing a little adjust on the AC-4 bias setting. Then I went to next step: TUNE UP ON DESIRED BAND. All controls were preset as the manual tells. Then I put the MODE switch in TUNE and got again the bias reading BUT I couldn't change this reading with the GAIN control, nor with the RF TUNE. Plate current remains the same, independent on GAIN and RF TUNE settings. So the question is: where should I look first for trouble?. I think this should be a very common trouble and, perhaps, it only indicates that the finals are shot. Anyway, I don't want to change them for the supossedly good Sylvania spares (these are not cheap tubes ;-) ) and then find another trouble which ruins them!.

By the way, the T-4XC under chassis is very clean and there is NO sign of burned components. And 6JB6 tubes have at least a good filament and they glow a _bit_ blueish inside the tube elements when you put the MODE sitch in TUNE mode. So there is at least some rest of life inside :-).

Thanks a lot for your help!.

Best regards.

JOSE


Date: Tue, 11 Nov 1997 14:32:55 +0100
From: JOSE V.GAVILA (EB5AGV/EC5AAU)
Subject: Re: Help: T-4XC no power output

Hello Don and all list members,

I have had a similar problem with the T4XC. The first thing that I did was to verify that the radio was working properly before it was shipped to me.
(snipped)

Well, I knew the transmitter DIDN'T work _before_ buying it, so I don't suspect of bad contacts. But the failure could be one or more bad tubes. I have checked most of them (swapping for good ones) without success. The only ones I have not changed are the finals; I only have two Sylvania NIB spares so I want to be sure that they are the culprits.

In 'spot' mode I get a signal in the R-4C receiver and in tune mode my FT-890 also gets some signal, but power output is almost zero.

Apart of the finals, I have something wrong in the AC-4: I get about 649VDC in the 650 VDC HV line, but only about 242VDC in the 250V line, and with 1.5VAC superimpossed... This is not in the 1/4% range the manual claims... This is in idle mode. If I put the rig in TUNE mode, I get about the same HV but only 220VDC, with 2.5VAC over it in the 250VDC line... So something is bad. Could it be the power supply filters?. I changed the HV (650VDC) capacitors, but not the 250VDC and BIAS capacitors.

Thanks for your help and best regards.

JOSE


Date: Tue, 11 Nov 1997 22:13:50 +0100
From: JOSE V. GAVILA (EB5AGV/EC5AAU)
Subject: Help: T-4XC no power output (II)

Hi gang,

Well, today I have found that I can get output in 80 and 40, but NOT in 20, 15 or 10... (I made all previous tests in 15 meters, so I thought all the bands were dead. WRONG!). Any clue?.

I have done the final stage tuning as per the manual, but found no mention about the maximum plate current the tubes can handle without damaging... In 80 meters I could get lots of power, but plate intensity went to the scale maximum... DANGER!. So, are there any other tuning procedures around, with clearer limits you should avoid?.

Please, be patient with me... This is my very first T-4 :-)!.

Thanks and best regards.

JOSE


Date: Wed, 12 Nov 1997 08:01:01 +0100
From: JOSE V.GAVILA (EB5AGV/EC5AAU)
Subject: Re: T4... tuning

Hi Art and list members,

I reproduce part of Art's message as I think it is very interesting for some of us:

Jose; When tuning the T4... you always have to keep in mind, that if the PLATE is not tuned to 'dip' in plate current, the plate current shouldn't exceed 0.15 A . In this situation, the whole power is dissipated in PA tubes and nothing is going out - it is 100W that is lost in heating the tubes. This is already too much for two 6JB6 but they can handle this for couple of seconds. All your tuning should be done at this plate current level. When you are tuned to resonance, then you can go up to 0.35 A with no problem.
(snip)

Thanks a lot for your comments!. Now I have got the idea: I should NEVER go more than 0.15A IF NOT AT RESONANCE and, once in resonance UP TO 0.35A. Well, I'm happy to know that, as the manual is not too clear on this, and tells to go to 'half scale' (0.25A!) and THEN look for the PLATE DIP. If you can do it in less than 2 seconds, it is OK but if you are a newcomer to T-4s (as I am), you can get in trouble!. Also, I have not found any reference to the 0.35A limit, so yesterday I put (ONLY few seconds) 0.5A in 80 meters... Full 200W!. So I suspected I was doing something wrong :-( .

Any further consideration to the tuning process?.

Best regards from Spain.

JOSE


Date: Tue, 09 Dec 1997 14:48:27 +0100
From: JOSE V.GAVILA (EB5AGV/EC5AAU)
Subject: T-4XC trouble (soft 6JB6s?)

Hi Drake gang!,

First than anything else I wish all of you a Merry Christmas and Happy New Year!.

Well, let's go on-topic... Some time ago I posted a message about my T-4XC troubles... Doing some further tests I have found that the transmitter works fine (full output) in 80 and 40, but it doesn't work in 20, 15 or 10 meters... I have some 6JB6 and 6GJ5 spares around, so I will try to find a matched pair and check with it. But before I do that, I would like to understand what happened to the current 'soft' tubes; why do they work fine at lower frequencies but don't work at higher ones?. Sorry if this is a too basic question, but I'm new to this problem!.

Thanks for your help and best regards.

JOSE


Date: Sun, 14 Dec 1997 01:20:36 +0100
From: JOSE V. GAVILA (EB5AGV/EC5AAU)
Subject: Drake T-4XC working ALL BANDS!

Hi again!

I got it :-)!. Now the T-4XC works in ALL bands, including 10 meters. All what it needed was a neutralization of the 6JB6 PA tubes to get it working after the RF / MIXER alignment done previously. By the way, the neutralization capacitor was only about 15 degrees out of adjustment but it makes a LOT of difference ;-)

I think now I have the full failure process for this unit:

1-Somebody decides the T-4XC is out of adjustment. Perhaps a 6JB6 or 12BY7 change?.

2-Trying to adjust the RF and MIXER trimmers, this guy shortcircuits one of the RF trimmers to chassis and... pffffff... two charred resistors (R38 and R39)!.

3-Probably the guy didn't found the broken resistors and, after some time 'adjusting' the RF and MIXER trimmers, he decided to sell the rig. Of course, the 'adjustment' left the poor transmitter far from its working point.

4-Then I bought a C-line with 'low power output' but 'with a couple of 6JB6 spares', as the seller thought the trouble was in the tubes... Now I have an spare Sylvania NIB matched pair :-).

The rest is already known by you...

Well, thanks again for all your help getting this transmitter to life!.

Best regards from a happy boy.

JOSE


Date: Sun, 14 Dec 1997 17:38:16 +0100
From: JOSE V. GAVILA (EB5AGV/EC5AAU)
Subject: A bit more on T-4XC work

Hi Drake gang,

Thanks for all your congratulation messages!. I appreciate them a lot.

Well, one thing I forgot to tell is that the alignment tool I used for the RF and INJECTION trimmers was part of my GC Electronics 'precision alignment tools for radio and television service engineers' 30 tools set. That tool is GC part number 8275. One side has an small standard plastic screwdriver, suitable for those trimmers which are easy to move (in my case, about 50%). But, for the harder to move ones, you need a metal instrument. A regular screwdriver is not suitable for two reasons: (1) it can cheat the adjustment, adding capacity due to its metal construction and, what is worse, (2) you can shortcircuit the capacitor under adjustment to chassis (which most probably caused the failure in my transmitter!). So the other side of the GC tool is an small metal blade encapsulated all around by a plastic cylinder. It is, viewed from the tip front, as an metal '|' inside a plastic 'O'. So, when you put it through the adjustment holes, you can't shortcircuit the caps to chassis, as the plastic prevents the contact. I hope the explanation is good enought... Sorry if it is not!.

Probably this is a very common adjusting tool, but I never had one of these until I got the GC toolset and it has proven really useful. So, if you don't have yet one, look for it at next hamfest!.

Ok, let's close the T-4XC thread :-). Hope you have enjoyed it as I did restoring to specs my unit.

Thanks again for your support.

*** MERRY CHRISTMAS! ***

JOSE


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