This is long - and you'll see why...
I posted a question about finding more bi-polar parts versus the MOSFET - seems that some of the locals here, want to use their "amps" that were designed more for the older Bi-polar versus the MOSFET repair redo's that a lot of the truckstop - radio shops - offer.
I will mainly be using this with my President Madison on side band. Would this be too much drive for it?
You bring up a good point...
Are you using a Bi-Polar? Does the Madison have the NFB on the 2166? OR, do you have the older 1306?
Either configuration - even then - it will need some method of NFB in the Pre-Driver or Driver to help with drive levels and the sheer dynamic range the power envelope will place on the input of the amp.
It's not the "Carrier" that kills these things (the pots I'm referring to) - its' the power of the envelope and all the spectral artifacts shoved into the coax going to that amps input is what burns these pots up. (Modulation is not excluded - it is the main portion of the problem)
The problems lies in how well the customer will follow instructions - you can put something together for them and it'll work great right out of the starting gate, but as time progressed - they had "this n' that" when "this happened" and "when I let someone borrow" CRUNCH - ow - that hurts...
So my "bulletproof" method was to pad - tone down - lessen - restrict - deny (insert favorite DO NOT DO THIS metaphor here) RF from perforating the finals or pots used in their variable setups - you already know from experience they will run hard over - hard over - 360 X2 rotation. So making it more of a mudduck style works for the guys and makes the shop happier from less electrical problems from the "problem childs" {note plural) they have out in the field. So they, aka "children" will turn their radios back up and harass the hell out of each other on the channels they run because of the stresses of doing the jobs they do - with heavy equipment.
So unless you prepared for the worst, some one was going to get hurt - then you get into those "wars" over it that are at times not unlike - Hatfields and McCoys type of feuds.
So that's where my mentor, friend, electrical repair guy played upon my insatiable desire to solve for an improper fraction and never leave a potential pot terminal - unterminated. That guy was also the supplier I went to for a lot of things. Fun days - shame that all that is from that time, is now gone, auctioned off - and I'm left with only the memories.
Protect your stuff - can't do a *amp thing about their stuff.
So that is why the open terminal in the box got sent to ground - but not directly - it was an operation parameter decision not just arbitrary. Sure - it lessens the drive level - a larger cap was used to absorb the RF as a shunt - and with some radios - like the 2510 or the TS5020 - their high-drive low-level modulation - you needed something to keep the finals from going to their reward, and from pinching up and FM-ing as any radio overdriving an amp will do. Did I save them any more money? Gawd I still have my kneecaps so I guess the blame went directed deflected to someone else. So, I think they enjoyed the rough housing they did, but if their equipment survived - I don't know. I see someone re-worked a section or two but the new owners want it restored to it's original - that's just the radio - who knows what happened to the amps. (none of my business)
And for your benefit, take the time to review the locations again, you placed two varicaps on two locations - I would have used them on the couplers caps in and out - to see if extra / less capacitance helps with the output matching of the amps own combiners. It's how I found out the 68pF was not enough to divert RF - at least wattage wise. I wanted them to have a good SWR over a larger range of power levels with less worry. I worked under the principle - Once that it got peaked, then work on the input drive levels and hope like h*ll the kids' gonna understand a simple rule of - it lasts longer if you don't over-do it. At least until the next paycheck...
Also - location - in your photo you use twins, 2 - 51 ohm and cap combos on the NFB between the combiners. I've seen values from 100 ohms to 39 ohms - good to see you keep it in there - many a tech does not - consider yourself a big plus in that category. I had to install them - I used 100ohm 2W and 0.001uF (102/100V) - so to help the kids with envelope - I kept the 75 ohms' - placing the active side to the open tab on the pot, kept the ground side (heat this ground side to allow the solder to liquefy and let you rotate that part without stressing and simply added/replaced where the 75s' active lead went with 150 ohm 2W carbon composition across to the ground leg of the 75 ohm until the SWR went nearly flat on the SSB mode (power dissipation inclusive) It's why I paralleled 3 of these 150 ohm resistors (6W capacity) there - it looked like hell but it worked. While they used it - which they used that button and they considered their amps to be clean (unpinched audio) and the variable, with the understanding that if the amps "cover" got hot, turn that knob down.
If they didn't - in TS amps - without the conversion I did, it was sure to blow their high-power finals in whatever their radios units they used, by the SWR issues it generates alone.
Also - remember the 39 ohm I mentioned a post or two earlier - there is a condition on that - it can be installed BEFORE it arrives to the pot, or cap or AFTER - the cap or towards the input combiner/splitter - you can play with that value and insertion location once you see where this is going.
That's where I'm at now, I depleted my supply - didn't imagine seeing some of the older radios' I did some work to, come back to have seen works' like new drop ins from someone else, then instructed to have it - removed - and returned to stock so they can, what they had back in the earlier times, back.
It's painful, but good to see them returned to stock portion, which is more of what I did to their stuff in the first place. They wanted/went back to simple tuneup and run with what ya' got stuff versus the newer flashy stuff. Seems the cost of replacement and the attempts to do-away with an extra stage amp - they wanted it (old style) back.
The pain from me is the effort I put into the audio lines, the coil - the bi-polar parts - all were dumped off into someones ashtray or trash bin with this new crap in it's place and I'm told to return it back to what it was...
It's not that easy when you're the one the depends on others that supplied locally - and now they are gone - not only to do you have to find a supplier - one you can trust to do business with without getting scalped in the process. And the ones that took your work for whatever reasons, to their benefit - now is dumped onto your lap and you have to do it all over again.
SIGH.
Oh well...Hi how are you? What's New?
:+> Andy <+:
