Collins 32S-3 Help

[WA6WWW]

I cannot get enough grid current. The mic gain is almost all the way open. I have plenty of plate current. The voltages in the power supply appear to be in spec. I have to turn the mic up almost all the way to get the ALC working. I do have a hum on the audio signal. All the tubes check out normal. I just replaced the 6146B's and the driver tube.

Dave Peterson
WA6WWW

[KC8VWM]

Hi Dave, Sounds like the caps in the power supply might need some attention. Do they visibly appear to be leaking? (Traces of white looking calcium around the base of the capacitor etc.)

[W3JN]

Do you get enough grid current in "tune" or "CW" mode?

The reason you're getting hum is you have the mic gain cranked all the way, and your mike might be bad or mis-wired, or there's a problem in one of the low level audio stages.

I'm concerned about your "plenty of plate current" statement. It should be at idle, per the manual, with the xmitter keyed in SSB and no audio. If not, you have other problems. Did you adjust the bias for proper idle current when you installed the new finals?

[W5HTW]

I agree with JN. If you can't get enough grid drive, how can you get "plenty of plate current?" It would seem the rig is not tuned properly. Be sure you understand how to tune it.

If you are getting high plate current, the bias is set wrong or is faulty, or the finals are not neutralized or are oscillating.

Why did you change finals? What was wrong with the old ones? Why not put the old ones back in and see what happens? That is, if they weren't shorted.

The high plate current is a problem. I believe the idling current should be 60 ma. That is with the PTT pressed and no audio into the microphone. If you are getting much higher than that, try adjusting the bias. If it doesn't bring it down, you have other problems, such as a faulty driver, faulty finals, or neutralizing is not correct.

Ed

[K9STH]

WWW:

First of all, what type is the neutralization capacitor in your 32S-3? This is the variable capacitor that is located inside the final amplifier stage between the 6CL6 driver tube and the 6146 final amplifier tubes. If your 32S-3 is one of the older versions this capacitor will be a ceramic trimmer. If it IS a ceramic trimmer then using the 6146B/8298A as final amplifier tubes WILL result in this capacitor "burning up". If the neutralization capacitor is an air variable then using the 6146B/8298A is OK.

If the neutralization capacitor is a ceramic trimmer then ONLY 6146, 6146A/8298, or 6293 tubes MUST be used in the 32S-3.

Next, did you neutralize the final amplifier tubes after changing them? If not, then you have to neutralize the new tubes.

Then, have you set the plate "idling" current to between 40 mA and 50 mA? If not, then you have to get this done. Basically, you put the transmitter in either LSB or USB. Then turn the mic gain control all the way counter-clockwise until it "clicks". Next, key the transmitter. Finally, adjust the bias control which is located on the 516F-2 power supply to show the desired current on the "plate" meter. Actually, the "plate" position on the meter reads cathode current.

After doing this, put the meter switch in the ALC position. "Un-click" the mic gain control but still leave it in the maximum counter-clockwise position. Lift the lid of the cabinet and locate the control on the chassis labeled "ALC". Key the transmitter and adjust this control for a "zero" reading on the meter. The meter can "pin" backwards when this control is not properly set. Or, it can read well above "zero". Again, adjust the ALC control until the meter pointer just "rests" on "zero".

When transmitting using LSB or USB the ALC meter really shouldn't read much, if anything. Using the "plate" position on the meter will give you a much better idea as to how the transmitter is performing. Basically, after tuning the transmitter in the "lock key" position adjust the microphone gain control so that your voice peaks do not exceed around 25 percent of the reading that you got when in the "lock key" position. A very occasional "peak" of up to around 30 percent is allowed, but not more. Since the meter movement in the 32S-3 cannot follow the voice peaks of the human voice you will not get a true reading except when there is a constant carrier and that happens in the "lock key" position.

You really don't need to keep an "eye" on the grid current. Basically, peak the Exciter Tuning with the meter in the "grid" position and the mode switch in the "tune" position. Keep this reading below maximum on the meter using the mic gain control. Then switch the meter to the "plate" position and the mode switch to the "lock key" position. Adjust the plate loading and plate tuning capacitors for the desired reading again holding down the drive by using the mic gain control.

When operating keep the meter in the "plate" position instead of the ALC position.

Now, there is one thing about the 32S-3 (in fact any of the 32S- series transmitters and the KWM-2 series transceivers) that needs to be checked. The meter "shunt" for the "plate" reading (actually reading cathode current) is provided by a total of 6 each 12 ohm 1/2 watt resistors from the 3 cathode connections within each 6146 series tube. That is, there are 3 of these resistors located on each final amplifier tube socket. In virtually every 32S- transmitter and every KWM-2 series transceivers, that I have worked on these resistors have changed value, almost always going "high" in value. Basically, you need to replace all 6 resistors. I replace the 1/2 watt resistors with 1 watt 5 percent resistors. The new resistors are about the same size as the original resistors even though they have twice the power ratings. Unless these resistors are changed, there is a very good chance that the readings of the "plate" meter are not going to be correct. Changing out these resistors is not difficult.

I purchase 12 ohm resistors in 100 quantity lots and keep them in stock to change out the resistors in every Collins 32S- series and KWM-2 series units that I work on. The Heath SB-Line transmitters and transceivers use 10 ohm resistors for the meter shunt and those transmitters/transceivers suffer from exactly the same problem as the Collins units.

Glen, K9STH
Technical Advisor Collins Collectors' Association

[WA6WWW]

Glen, Thanks for the reply. Can we trade emails? It might be more efficient. Backing up a little, I was tuning the transmitter when I had a "power surge", the watts out jumped up to over 200 watts and blew the fuse in the 516F2. Not finding any problem in the supply I replaced the zener diode with a standard one, just cuz. Because I had the lack to grid current when in the lock-key position I traded out the driver and the 6146B's. But I still have the same problem. It always has tuned with the mic gain about at the 12 o clock position. But now I have to get it to the 3 o clock position to get any reading on the grid. I have 230 ma on the plate. The neut cap is the air variable. The no sig plate current is set at 40 ma per the manual. I can operate but I have hum on the voice sig.

Dave

[K9STH]

First of all, there are no zener diodes in either the 32S-3 or the 516F-2! The original 516F-2 had a selenium rectifier ("diode") as the bias rectifier and the later versions have a silicon diode as the bias rectifier. You can replace the selenium rectifier with just about any silicon rectifier with a PIV of 400 volts or more. I just use a 1N4007 because they are really cheap and have a PIV of 1000 volts and a maximum current rating of 1 ampere.

It sounds like you have lost at least one, if not more, of the electrolytic capacitors in the 516F-2. You can get replacement capacitors from Mouser for less than $20 total for all of the capacitors in the 516F-2. I would suggest replacing all of them, both the high voltage and the bias voltage capacitors.

By the way, you DO still have the 5U4 and 5R4 rectifier tubes in the 516F-2. If, for some reason, you have replaced them with solid state-devices there is a very good chance that the electrolytic capacitors have gone bad. Between the higher voltage from the solid-state devices and the higher ambient line voltage from most electric companies in the United States (most now run 125 VAC +/- 2 volts with things generally being on the "+" side especially during the warmer months) the voltages can easily exceed the working voltage of the capacitors.

There won't be much grid current showing in the "lock key" position. It is when the mode switch is in the "tune" position that you should show grid current and that is primarily for the purpose of tuning the "exciter tune" control. I know that the manual says that you should show about 1/2 scale when in the grid position when the transmitter is in "lock key". However, most 32S-3 transmitters don't have anywhere near that much grid drive. Basically, if you can adjust the microphone gain control for a reasonable "plate" current that is all that is required.

You need to check the coupling capacitor between the plate of the 6CL6 and the grids of the 6146 finals. This is a 4700 pf and they have been known to fail. Also, there are additional neutralization capacitors for the driver on the underside of the chassis (ceramic trimmers). These have also been known to fail and can produce a "power surge".

Again, have you neutralized the driver and finals? You need to either disconnect the heater voltage on the driver or else use an old tube with one of the heater pins removed. Also, you have to remove the screen voltage jumper which appears between the center pins of 2 of the RCA phono jacks on the rear panel. Most people just make a jumper using 2 RCA phono plugs to restore this connection rather than replacing the jumper on the inside.

You can contact me by E-Mail at

k9sth (at) sbcglobal (dot) net

Glen, K9STH

[WA6WWW]

Glen,

You are a wealth of information. Yes, I used 1N4007. I have tubes for the rectifies and not solid state. It seems from what I have read most of the problems with this xmtr go back to the power supply. I will go and replace all the caps in the 516F2. I have not tried to neutralize the finals yet. I will also check the coupling capacitor between the driver and the finals. I will report back after Mouser make the delivery. Thanks again.

Dave

[WA6WWW]

Glen,

Two additional questions. I checked the voltages under a no load condition and got 1,000v, 275v and -80v. These voltages seem in line to me. Is it possible that the power supply caps are still bad? How do I check that little disc cap C60?

Dave

[K9STH]

First of all, it is NOT a good idea to operate the 516F-2 with no load. The peak voltage can exceed the ratings of the capacitors.

For the disc ceramic capacitor (4700 pf) just replace it. They are cheap enough and are very difficult to actually check.

As for the electrolytic capacitors: The electrolytic solution eventually "dries out" over time and the capacitors in your 516F-2 are going to be at least 40 years old and it is even possible that they are 50 years old. Again, new capacitors are inexpensive and I definitely suggest just replacing them. For the 2 section "can", just leave the "can" on the chassis but disconnect the wires from it. Then install individual capacitors under the chassis to replace the ones in the "can". New capacitors are considerably smaller than the originals and there is plenty of room under the chassis to replace the capacitors. Also, use 450 volt capacitors to replace the original 400 volt capacitors this gives an additional "safety factor".

Replacing the capacitors is cheap insurance against failure. Even if some of the original capacitors are still good, they WILL go bad and that will cause more problems, even the possibility of a shorted power transformer.

Glen, K9STH