Discussion in 'Amateur Radio Amplifiers' started by WA6MHZ, Jul 31, 2017.
I wonder who that was?
You were attracted to the thread like a moth to a light.
You take correctly. Yes
My name sake Uncle once told me "Lend many thine ear and few thy mouth" but sometimes ya just got to speak up.
Pickle jar is better. Mayonnaise turns rancid pretty quickly, but pickles don't.
Meanwhile, back here at the Radio Hospital, work progresses. Yesterday I tore out the forlorn Tuning variable to see if I could file the pits away. I filed all afternoon until the Nun came and told me it was time to take her to RUBIOS. (IT WAS TACO TUESDAY!!!) So I left the variable on the desk and returned this morning for more filing. I was carefull to round the edges where had filed. But since these plates are firmely attached to the rotor and stator, they cannot be removed for precision work. I filed them as best as I could and said "THAT WILL HAFTA DO". Since these variable are UNOBTANIUM we will hafta NURSE this one along.
IT might work. I Noticed the LOAD CAP is completely different than the one I just used in the SB-226. (IT WAS A SB-221)
This old SB-220 has what looks like a Broadcast variable in it.
Next I reinstalled the front panel and yanked the cap bank. those will all be replaced with new caps.
so now I gotta make the BIG MOUSEYWOUSER ORDER!!
Here could be why the PS BLEW UP. Notice the lead on the bleeder resistor
NO WONDER It CAUGHT FIRE!!!!
Pat, The SB-220 used two different load caps and three different tune caps in it's lifetime, including the SB-221 and HL-2200 which are only later versions of the SB-220. First for the load caps. The early SB-220 and even SB-200's used the same broadcast type load caps. Later models including the 221 and HL-2200 and SB-201's moved to the more conventional type cap. As far as the three types of tune caps. The first two types are the shorter and closer spacing 250pf types. One kind had removable plates that can be changed if the plates got burned and the other non-removable plates (which looks like what you have there now) And the third type is a longer footprint with wider spacing and removable plates as found in the SB-221 and HL-2200. When I run into a unit in for service that has burned plates I, just replace the burned plates on the removable type caps. On the non-removable type I just replace the cap with a good one of either type I have on hand. With a unit like you have I would file the plates and use it for a load cap on a 6 meter conversion. It will never arc. However reusing a filed unit for a tune cap my be asking for problems. It is a crap shoot. I fully stock new rectifier boards, soft keys, filter caps, bleeder resistors, relays, good load and tune caps, common resistors, capacitors, didoes switches etc. I rarely if ever have to wait for any parts. Having all the parts needed at your disposal makes a full restoration of an SB-220 a one day job.
Pat needs to talk to you.
Your are the second person in the last 24 hours to tell him not to attempt to rehab that tune cap.
(I was the first.)
Those electrolytics look pretty sad to me too. (OK, I'm a back-seat driver...)
Deep Fried Pickles! YUM
In other amplifier news, we were greatly dismayed to find that the W7RY softkey board would not work in the SB-200.
Being a DESIGN ENGINEER, I have the Technology to come up with a circuit that WILL work.
Despite a "IT WILL NEVER WORK" comment. I pushed on and decided to use the FILAMENT voltage to get the voltage for a relay control circuit.
But the voltage is ONLY 3.3VAC to ground on the Filament choke. HMMMMM
ALL I NEED TO DO IS use a voltage multiplier circuit!!
I robbed the Voltage QUADRUPLER circuit, built it and VOILA!!!!
I have 13.8VDC ready to run the relay keying circuit!!!
The keying circuit didnt work like I wanted however. But after MOUSING around with it, I have it working great!!!
somewhere the circuit is botched, and the relay is keyed, but a ground at the relay terminal unkeys the relay and the contact is closed for the big relay! I see only 0.7VDC on the key terminal!!
the circuit was wired in
the green wire goes to the filament winding on the back panel. And we can see the 33 ohm that normally went to the key jack now goes to the relay contact
So lets look inside.
I was most pleased to find CETRON TUBES which means the SB-200 is probably good. Cetrons are BULLETPROOF!!!
in the power supply compartment we found the stock board up graded to new caps and 100K bleeders. but the meter didn't have a DOUBLE back to back diode so I installed that. SB-200 meters are unobtainium too.
So when Sue comes Saturday, we will install the 4.7M resistors and the SB-200 should be good. I DO Need to get a stock SO239 and replace the stupid RCA jack on the input. Maybe I need to remove the tubes to install the jack, as the drill vibration might damage them.