HR2510 final, from MRF477 to 2sc1969

[Xracerx13]

I have a thing you can do to get more input power to the final without changing or buying anything. Try this first. Its a better ground for the driver, thats it. Trust me.

What you need is a piece of solid wire like from a resistor. Your gonna attach it to the emitter of the driver and then run the other end to a better ground area. The reason I do this is when I remove the two 560pf caps from the final legs and then add an insulator behind the MRF477 the power output drops to about 18 watts pep. With the addition of this ground the power is right back up to where it should be. Obviously in the picture it is the wire covered in green heat shrink.

 

[Cable Guy]

I have a thing you can do to get more input power to the final without changing or buying anything. Try this first. Its a better ground for the driver, thats it. Trust me.

What you need is a piece of solid wire like from a resistor. Your gonna attach it to the emitter of the driver and then run the other end to a better ground area. The reason I do this is when I remove the two 560pf caps from the final legs and then add an insulator behind the MRF477 the power output drops to about 18 watts pep. With the addition of this ground the power is right back up to where it should be. Obviously in the picture it is the wire covered in green heat shrink.
View attachment 73068

I will try that for sure thanks.

 

[Xracerx13]

I will try that for sure thanks.

You could also add a 220pf cap across C126 to bump up the input to the final. But I think the extra ground I mentioned should be enough.

The 2 larger torroids I believe use 24ga wire, but I use 22ga when I re-wrap them.

 

[Xracerx13]

Interested to hear which way you went. The ground wire or the 220pf cap? and how it turned out for you.

 

[Cable Guy]

Interested to hear which way you went. The ground wire or the 220pf cap? and how it turned out for you.

I haven't got it back on the bench yet, awaiting magnet wire, but I will put it out today and try your suggestions.

 

[Cable Guy]

Interested to hear which way you went. The ground wire or the 220pf cap? and how it turned out for you.

I tried both and neither increased output at the moment. I really think the toroids are at fault. I will try the ground and cap again after those are rewound. Thank you Xracerx for the ideas. I'm curious what you have going on in that pic with the cut trace, ceramic and silver mica cap and resistor.

 

[Cable Guy]

I removed the toroids and cleaned off the windings, separating them a little so they don't short. I put them back in, tweaked vr107/vr103, since I expect half the output of the 477 I set vr103 at 10 watts using cw, and now get an am dead key, adjustable with vr107, from 0 to 8 watts. Am avg output swings backwards when set at 5 and up, and peak (marked as pep on my meter, but isn't true) when set at 4 watt dk, is about 8. Ssb pep is around 13 watts.

Most everything I have experience with is high level modulated, not low level like these rigs. I noticed some vr's are erratic so I will change them I think. I may also now try Xracerx's c126 cap increase again. I did pull the pre-driver 2sc1973 and test, it had a gain figure of 63. I gotta go look up the spec now.

 

[Xracerx13]

I'm curious what you have going on in that pic with the cut trace, ceramic and silver mica cap and resistor.

the cut trace and the little cap and jumper is a Rogerbird hi-power mod. https://rogerbird.tripod.com/2510betterhi.htm
or

Thread 'Stupid HR2510 Mod what is it?'

Jan 26, 2022

I dug out another from the bottom of the pile and I could not get it right until I removed this mod. I have seen it before. And have 3 radios in my parts radios with this same mod. Funny the mod mind not be too good. All 3 radios in the parts pile are pretty toasted. So here is a picture of the mod. Model, unmoved and screwdriver pointing to another trace jumped in the mod. By the way this is something to do with the pre. predriver.Q134.

• Low_Boy
• Replies: 7
• Forum: CB Radio Modifications

Pay no attention to the resistor. Thats for more drive to the driver to get more power out of an MRF455 or SD1446. If you do the Rogerbird mod with the cut trace, you should see more pep on SSB. Seein how its a 1969 final.... 4 watts deadkey is the max you should go. Its unfortunate but it is what it is.

 

[Cable Guy]

I have an issue with another 2600 using an mrf477. While unkeyed I saw 21ma current draw when attempting to set final bias. It should be zero until I key in ssb. With radio unplugged I checked resistance between final bias test point and ground. I got 220 ohm. I thought maybe I had a bad capacitor to ground but no. I already rewound the toroids and cleaned all glue so no leakage there. I isolated the collector of the final and read about 220 ohms resistance between collector and emitter (ground). Is this junction leakage? Will the mrf477 need to go?

Edit: after some research, it looks like this transistor is bad. Too bad, I can factor the 20ma leak into bias adjustment, set it for 70ma and get about 25 watts out, but I imagine it won't last.

 

[Cable Guy]

Oh, the wire on the small toroid is 30ga, the medium toroid is 26ga and the 2 large toroids is 24ga.

 

[Cable Guy]

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

Thinking of trying out the mosfets on these rigs with weak/bad finals. Is that the Jackson mod for changing the mrf477 for an irf520? What kind of power did you see? I was referencing the posts at another forum:

HR2510 MOSFET FINAL - Page 2 - Transmission1

 

[9C1Driver]

Too bad HG doesn’t make a mrf477 replacement, it’s just feels wrong to have to have a conversation about a mosfet mod for these great old radios. At this point it’s probably the only option left to keep them going.

 

[Cable Guy]

Too bad HG doesn’t make a mrf477 replacement, it’s just feels wrong to have to have a conversation about a mosfet mod for these great old radios. At this point it’s probably the only option left to keep them going.

Rfparts.com has the 497 but at $62+ it's not in the budget. I think I saw a matched pair of 455's somewhere but those were right up there at over $120. I have 2 HR radios that need finals and the owner won't pay for the right stuff, would rather pay me just as much to retrofit a mosfet and get less power. Make it make sense.

 

[SuperLid]

Too bad HG doesn’t make a mrf477 replacement, it’s just feels wrong to have to have a conversation about a mosfet mod for these great old radios. At this point it’s probably the only option left to keep them going.

They do. It is trash.

 

[SuperLid]

Thinking of trying out the mosfets on these rigs with weak/bad finals. Is that the Jackson mod for changing the mrf477 for an irf520? What kind of power did you see? I was referencing the posts at another forum:

HR2510 MOSFET FINAL - Page 2 - Transmission1

I have done it on a Jackson as well. FYI, the original article you linked to by ashtec, has errors.

I did this first with IRF530, then IRFZ44. The measured power out from IRF530 is in my post on there. The power out with IRFZ44 is almost the same as MRF477. Perhaps slightly lower on SSB, but not enough for me to worry about. Like I said in my post on there, the HG part is junk.