Al,
Thanks for the information. I will note it for furture projects. I have already finished building my 30 watt amp last August and have been using it a lot since then. It realy works great.
Pete
AB2KG

To AB2KG and others looking for Teflon coated wire in various sizes-
RF Parts sells this wire in 10, 50, 100 and 500ft lengths. Ordering it from them will help meet the ridiculous $25.00 minimum order requirement.

Hook up wire should be stranded for it's flexibility. Radio Shack sells it. #22 is good for signal levels or low power... use heavier wire for high current circuits.

AL - K8AXW

I picked up a used Yaesu FL-110 amp, so I do not need to finish this amp project...

I have an ALMOST COMPLETE "kit of parts".. all that I lack are the toroid cores.

I forget how much I have in this project so far, but if someone were to make a FAIR AND RESONABLE offer, they might have a head start on parts collection.

bob K8YS k8ys@arrl.net

I am presently obtaining parts/boards, etc. for this "winter project."

The unit described is for SSB but I would like to know if any mods or bias changes need to be made to use it on CW?

73

AL

    How important are the ferrite beads (not mentioned in the text or parts list) to the functionality of the amplifier?

The T-50-2 cores for 160M and 80M are wound with the #24, 30 turns and 22 turns respectively. The remaining T-50-2's and the T-50-6's are wound with #22. You can find this documented in the handbook project from this filter was taken.
Pete
AB2KG

Why did AMIDON send me a equal lengths of #22 and #24 wire?
The instructions say #22, but there is not enough of it to finish.

Jim,
I have replaced both transistors and added a thin coating of thermal grease between the large heatsink and the top of the chassis. The amp tuned up fine. Last night I put in the filter board and measured about 38 watts out on 40, 30, 20 and 15 meters (the four bands my K1 uses) into a 50 ohm dummy load. I'm looking forward to trying it on the air this weekend. Thanks again for a great project!
David

Jim,
Fortunately I can still hear the relay switch in when I ground the PTT. The plastic washer/spacer in the tab of Q3 is the only part that shows visible heat damage. The amp is drawing very little current, whether idle or in transmit mode. I have ordered replacement transistors for Q3 and Q4 (along with a few extras) from RF Parts. Since the vendor has a minimum purchase requirement I also picked up some heatsink grease and a "Feedback Mod Kit for solid state amps", among other items. After I have the amp properly tuned and tested for normal operation, I thought I might try the feedback modification. Do you recommend putting a film of grease between the heatsink and the chassis, or is that unnecessary?
I'll let you know how it works out.
Thanks again for your advice.
David

David,
The amplifier has no VSWR protection, as you discovered. The ~~100 watts is likely your meter summing the forward and reflected power. In any case, how much current are you drawing at idle? If it's high at least one of the transistors is likely damaged (shorted), if not, it's still possible that they are bad. You can try an ohm meter check or simply replace them. Check for damaged parts - overheated resistors, etc. Also, check that the relay is functioning, perhaps you've 'welded' the contacts.

Good luck!

Jim

Jim,
This evening I decided to re-tune the amp as a practice run for a demonstration at my ham radio club. When I keyed down, the needle on the meter shot past 40 watts and looked like it was near 100 W. I quickly released the key waited a minute, then keyed again. This time the needle was far below 40 W and I noticed very high SWR. I took my dummy load apart and found that the ground wire from the resistors to the BNC connector had become detached. I repaired the dummy load and now have practically no SWR, but the power output of the amp is about 1 to 1.5 W.
The plastic mounting kit washer/spacer that goes into the center of the tab on Q3 looks like it was partially melted, though the multi-meter tells me that the tab is still insulated from the mounting screw (i.e., not grounded by the screw to the chassis). I suspect however, that I may have fried the transistor. Does this seem like a probable diagnosis? Is there some other place that I should look for the problem (i.e, other parts that are likely to need replacing)? I notice that the plastic washer/spacer in the tab of Q4 looks undamaged.
Thanks for any suggestions.
David

David,

Looks as though you are making progress! I agree, the thermo pads are a lot easier to work with than the thermal grease. Ok on the V+ wire ... that will help! Welcome to the club - we've all done something like that.
Ok on the power ... it will drop off with the filter card in place once the harmonic content is under control. The pot doesn't require to much adjustment, seems about right.

Jim

Jim,
    Thanks for your reply. I have replaced the mica insulators with the thermal pads (I didn't want to mess with grease).
    After reviewing the schematic, it suddenly occurred to me that I had forgotten to run a wire from the power switch to the +V pad on the circuit board (of course, I feel very foolish over this). After doing so, the indicator LED's functioned as expected and I proceeded to tune-up.
I only had to turn the potentiometer about 35 to 40 degrees from ground position to achieve a 15% power increase. Further adjustment did not yield any increase in power. My meter (not the most accurate) read about 40 watts on 14 MHz with 2 W drive at 14.7 V dc. The QST article gives an approximate 35 W output, so I guess I'm in the ballpark. Does the potentiometer adjustment sound about right? I was surprised that it took relatively little adjustment.
    The next step is taking readings with the filter board in place. Now that I can see the light at the end of the tunnel, I'm starting to feel some sense of accomplishment and am excited about getting this project on the air. I'll be using it with an Elecraft K1.
    Thanks again for all of your help.
David

David,

When mounting the TO-220 packaged transistors, do the thermal insulator pads go between the transistors and the mica insulators, or between the mica insulators and the chassis?

WITH THE THERMAL PADS YOU DON'T NEED THE MICA INSULATORS. IF YOU HAVE ONLY THE MICA BE SURE TO USE SOME THERMAL GREASE.

I realized, after I had mounted the transistors, that I had left these off. It's going to be difficult to get them in place now.

When I turn on the power switch, the Transmit LED (green) lights up along with the Power LED (red). This happens even though I have not externally grounded the PTT circuit and have no RF input connected. I've used my multi-meter to check the wiring but can't find anywhere that it is grounding the PTT. Any suggestions?

THE 'LOW' SIDE OF THE RELAY MUST BE PULLED TO GROUND SOMEHOW. ON A LOW RESISTANCE RANGE MEASURE FROM THE C7 SIDE OF THE RELAY TO GROUND - WHAT DO YOU SEE? SWITCH THE METER TO A VOLTAGE RANGE, TURN ON 12 VOLTS TO THE AMP AND MAKE THE SAME CHECK - YOU SHOULD SEE 12 VOLTS. IF IT'S NOT 12V, LOOK FOR A SHORTED COMPONENT - C7,10,20 OR Q1. IF YOU SEE 1.5 - 2 VOLTS, CHECK TO SEE OF D1 IS BACKWARDS.

JIM



Thanks,
David

When mounting the TO-220 packaged transistors, do the thermal insulator pads go between the transistors and the mica insulators, or between the mica insulators and the chassis? I realized, after I had mounted the transistors, that I had left these off. It's going to be difficult to get them in place now.

When I turn on the power switch, the Transmit LED (green) lights up along with the Power LED (red). This happens even though I have not externally grounded the PTT circuit and have no RF input connected. I've used my multi-meter to check the wiring but can't find anywhere that it is grounding the PTT. Any suggestions?

Thanks,
David

The FARA TekTalk pages have been updated with a copy of the QST article (reprinted with permission), along with an updated parts list and PDF files for the drilling templates.

Jim