HR2510 final, from MRF477 to 2sc1969

[Cable Guy]

So a friend has a cache of these 2600 and 2510 president radios and I have been cleaning glue, recapping and most recently, replacing a final in one with a 1969. Online resources say to remove the 2 560pf caps across the final, set bias to 50 and go. Well, that only nets me about 10 ssb pep, 1 watt am peaking 4. I was expecting 18-20 ssb pep and at least 4-12 am. Anything I'm missing? Do the input/output networks need some more work? I know the 1969 isn't optimal but better a 4 watt radio than no radio, right?

More info, I only know the final was bad, showing as 2 resistors, I don't know the circumstances surrounding the failure. I didn't test the driver as the voltages and idle current are correct, and it is amplifying. After replacing the final, voltages and idle current are in spec, and it is also amplifying.

 

[sp5it]

did you cross the legs?

 

[Cable Guy]

did you cross the legs?

Yes sir. I also added an insulator.

 

[brandon7861]

Is it possible that with the different transistor, the impedance match (green) into the filter is wrong? Are L17 and L18 adjustable? Peak those if you can.

If that don't work, maybe you could you decrease the negative feedback on the driver and/or final by increasing the value of the feedback components (red). It might make it unstable, watch for self-oscillation. Adjust the one doing the least gain first.

 

[nomadradio]

L17 and 18 are toroid transmission-line transformers, each with a two-to-one voltage step up from the final's collector to the antenna jack. Becomes a 16-to-1 impedance step up overall.

The enamel insulation on the toroids' wires is suspect. If it overheats or the brown glue eats through it you will lose power. Rewinding it is no big deal if you have the enameled wire handy. The wires get twisted together, wrapped around the core and then wired in series. This has been the mystery fault in more than one weak 2510 we've seen.

73

 

[brandon7861]

Thats cool, I haven't seen that before. Must be what the dotted circle means. Not adjustable then.

I'm curious though. Wouldn't it take a 4:1 voltage ratio for a 16:1 impedance ratio?

 

[nomadradio]

Yeah, two to one in the first toroid, then feeds into the second two-to-one transformer.

73

 

[brandon7861]

Im an idiot lol, thank you!

 

[Dr. Frankenstein]

I thought I had read somewhere a very long time ago that the final to use, instead of the 1969, was the 1945 due to the the legs being the same as the 477.

 

[Cable Guy]

Is it possible that with the different transistor, the impedance match (green) into the filter is wrong? Are L17 and L18 adjustable? Peak those if you can.

If that don't work, maybe you could you decrease the negative feedback on the driver and/or final by increasing the value of the feedback components (red). It might make it unstable, watch for self-oscillation. Adjust the one doing the least gain first.
View attachment 73053

I did play with cap values along the way, some very minor increases, mostly just put it back like it was afterwards. Yeah, nomad knows, these toroids are what they are. I got the glue out, but it's very possible that some enamel got removed from the corrosive glue and my cleaning efforts.

 

[Cable Guy]

L17 and 18 are toroid transmission-line transformers, each with a two-to-one voltage step up from the final's collector to the antenna jack. Becomes a 16-to-1 impedance step up overall.

The enamel insulation on the toroids' wires is suspect. If it overheats or the brown glue eats through it you will lose power. Rewinding it is no big deal if you have the enameled wire handy. The wires get twisted together, wrapped around the core and then wired in series. This has been the mystery fault in more than one weak 2510 we've seen.

73

You may be right. I will order some wire, I might have some already just sitting around in a transformer somewhere, gonna have to mic the wire from the toroid and see if I have something the same diameter. Thank you.

 

[Cable Guy]

I thought I had read somewhere a very long time ago that the final to use, instead of the 1969, was the 1945 due to the the legs being the same as the 477.

Yeah, but I think the 1945 was a weaker part, like 12 watts or thereabouts, and just as hard to find as the 477. The leg crossing isn't that hard, just doesn't look pretty.

 

[SuperLid]

So a friend has a cache of these 2600 and 2510 president radios and I have been cleaning glue, recapping and most recently, replacing a final in one with a 1969. Online resources say to remove the 2 560pf caps across the final, set bias to 50 and go. Well, that only nets me about 10 ssb pep, 1 watt am peaking 4. I was expecting 18-20 ssb pep and at least 4-12 am. Anything I'm missing? Do the input/output networks need some more work? I know the 1969 isn't optimal but better a 4 watt radio than no radio, right?

More info, I only know the final was bad, showing as 2 resistors, I don't know the circumstances surrounding the failure. I didn't test the driver as the voltages and idle current are correct, and it is amplifying. After replacing the final, voltages and idle current are in spec, and it is also amplifying.

I have been successful enough, going from MRF477 to MOSFET. Power output was close enough for my liking.

 

[Cable Guy]

I have been successful enough, going from MRF477 to MOSFET. Power output was close enough for my liking.

I think I saw your post about that on another forum, it was certainly a good option given the lack of good alternatives. That post is what I used as a guide to the bipolar swap. Thanks.

 

[Cable Guy]

Does anyone recall the gauge of wire on the 4 toroids? I think I will just order some magnet wire to rewind them. Looks like maybe 2 or 3 sizes.