What's the purpose?

[GnG8d]

I have a SB200 tore down and I noticed that someone pulled a 68uuf cap off of ground, and then jumped the 10m input coil with a 100uuf cap. Exactly what did they think they were gaining?

 

[Captain Kilowatt]

What were gaining? How about an input tuning network that tuned 11m instead of 10m.

 

[GnG8d]

forget i said that :headbang:

 

[Captain Kilowatt]

forget i said that :headbang:

Said what? Did somebody say something?

 

[mackmobile43]

How soon we forget.

 

[VA3ES]

I always thought that there was enough latitude in the stock tuning network to cover 11M?

 

[Beetle]

SB-200 is a pretty old amplifier. Normal parts tolerances plus 20-30 years could account for that.

 

[VA3ES]

SB-200 is a pretty old amplifier. Normal parts tolerances plus 20-30 years could account for that.

Except that coils don't deteriorate, and silver micas are pretty stable, unless they suffer from silver migration, which would cause a short in the cap.

 

[Captain Kilowatt]

I just figured 11m, maybe he was going for 12m.

 

[wavrider]

Keep in mind the SB200 was designed to be used with tube rigs per say, The transciever had a plate and load so it could match a broad range.

Todays solid state rigs do not like the high VSWR input of the SB200, especially on 10 and 15 meters. 20 through 80 can usually be tuned with the slug to give a decent input vswr.

Google SB200 mods, Some dutch amp guru has a great sight on reworking the input section of that SB200. Rewinding the 10 meter coil and changing a few caps to different values. Now my SB200 has a nice 1:1 input and covers the entire band with less than an 1.8:1

sb200eng
There is the link, I followed the mod for the input, worked great.

 

[GnG8d]

I just figured 11m, maybe he was going for 12m.

Probably is 11m, to bring the loading knob to vertical :shrugs:

 

[GnG8d]

sb200eng
There is the link, I followed the mod for the input, worked great.

Thanks for that link, I'll read it tonight. I'm looking for a parasitic choke design too, I'm not going to use the Rick Measures choke design.

I decided to go through this thing from the power cord to the antenna jack with the schematic and a meter. As beetle said, these 40 year old carbon composite are all being replaced with new carbon composite in the RF cage, and a mix of ceramic composite and metal film elewhere. There are only a couple electrolytic caps outside of the power supply, but those are being changed out as well (filter caps and bleeders are already updated). I'm spot checking a few mica caps, but I'm not too concerned with them.

Anyway, with my head buried in the amp, I couldn't see the forest for the trees, the amp came from a CBer, so I'm sure it's 11m meter tuning, but yes mack, it could be old age creeping in :blink: