4 x MRF422 (HG's) update.
Good so far! I'm pleased about the reduced current demands for similar PO. I had 2879's in this amp when new and it was way too much for my PSU. Although my 28v PS has bigger iron than a 35A Pyramid/Astron, it still fits inside the 35 chassis. I don't think it could provide much more than 40A tops.
After trying many combo's of ceramic variables and mica-dipped, I finally saw nearly 300W AM carrier driven with a Radio Shack TRC-451 on 12v into a DL. That's with 26v to amp, drawing a bit over 20A.
Settled on 470pF on the Base side of Input Transformer; 1120pF on Collector side of Output Transformers. Placed Trimmer caps (115-400pF) before Input Combiner and after Output Combiner with mica padders on each (33pF and 90pF respectively. Trimmers have room above & below.
Bias Circuit: 750mA fuse at bias source, near relay. Blew fuse once when adjusting the 10T Bias pot but not since. Max current limited to 3A rating of MC78T15 (TO-220 V regulator) which feeds an LT1003 (5v regulator/TO-3 package) then to a shunt regulator (4 x 1/2W, 20ohm resistors at each base). 0-1v panel meter proving helpful. When I applied the formula for estimating base current (ifwtech.co.uk/g3sek/tr-bias/tr-bias1.htm) I determined max current peaks should be less than 2.8A. Fuse gives peace of mind.
It's a truck stop amp. It may have through-hole plating but the pcb is paper thin so each component change requires patience. Although it makes RF, I'm not sure where, lol. I need an SA I guess. I see Ebay has small SA's for $70. Are they worth it?? I can't afford much more and Wife gives me grief with each piece of new equipment.
I tried more drive (18W ssb 'Dial a watt" sans FT-891) made current peaks exceed 40A which at 26v is a lot. Likewise, the PO jumped way up. My only watt meter is a RS 2KW watt meter/swr combo but its a good ballpark indicator. On the Yaesu, amp does not like 20M but sings on 40.
I want to thank all the members that answered my many questions since I began moving to 28v 2 years ago. This is a wonderful forum.
Neil, NYC
N2EYE
Good so far! I'm pleased about the reduced current demands for similar PO. I had 2879's in this amp when new and it was way too much for my PSU. Although my 28v PS has bigger iron than a 35A Pyramid/Astron, it still fits inside the 35 chassis. I don't think it could provide much more than 40A tops.
After trying many combo's of ceramic variables and mica-dipped, I finally saw nearly 300W AM carrier driven with a Radio Shack TRC-451 on 12v into a DL. That's with 26v to amp, drawing a bit over 20A.
Settled on 470pF on the Base side of Input Transformer; 1120pF on Collector side of Output Transformers. Placed Trimmer caps (115-400pF) before Input Combiner and after Output Combiner with mica padders on each (33pF and 90pF respectively. Trimmers have room above & below.
Bias Circuit: 750mA fuse at bias source, near relay. Blew fuse once when adjusting the 10T Bias pot but not since. Max current limited to 3A rating of MC78T15 (TO-220 V regulator) which feeds an LT1003 (5v regulator/TO-3 package) then to a shunt regulator (4 x 1/2W, 20ohm resistors at each base). 0-1v panel meter proving helpful. When I applied the formula for estimating base current (ifwtech.co.uk/g3sek/tr-bias/tr-bias1.htm) I determined max current peaks should be less than 2.8A. Fuse gives peace of mind.
It's a truck stop amp. It may have through-hole plating but the pcb is paper thin so each component change requires patience. Although it makes RF, I'm not sure where, lol. I need an SA I guess. I see Ebay has small SA's for $70. Are they worth it?? I can't afford much more and Wife gives me grief with each piece of new equipment.
I tried more drive (18W ssb 'Dial a watt" sans FT-891) made current peaks exceed 40A which at 26v is a lot. Likewise, the PO jumped way up. My only watt meter is a RS 2KW watt meter/swr combo but its a good ballpark indicator. On the Yaesu, amp does not like 20M but sings on 40.
I want to thank all the members that answered my many questions since I began moving to 28v 2 years ago. This is a wonderful forum.
Neil, NYC
N2EYE
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