anyone have a full schematic for a mohawk 10 5b. no driver plate current reading on transmit.trying to make it easy on myself before I take it apart. all new tubes. 3 mica dipped caps on input relay board dark in center. any help would be great. thanks soretooth
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mohawk 10 model 5b
- Thread starter soretooth
- Start date
arcing on first section of a/v load cap. very close spacing, going to clean them up and try again. deadkey 5 watt input 400 watt output no swing with audio input. still don't have the full 40ma on driver. I will keep this post updated just so folks can read it.
If you haven't found a sche for it yet, try here: http://www.cbtricks.com/Amp/mohawk_10/5B/graphics/mohawk_5b_sch.pdf
I have seen those old Mohawks on the auctions sites, all I have seen have been rough shape.
The year of manufacture almost guarantees all the capacitors in the amp need to be replaced as do the resistors need to be unsoldered from the circuit and measured, replaced if necessary.
I could not see how the 572'bs were biased in the link to the schematic but 400 Watt dead key is rather much, as the 572b is rated at 300watts output.
They look like great old low drive tube amps, and both tubes are still available as the 6146 is a popular tube in old hybrids.
Get some pictures if you can. Happy holidays
Thanks Alasta and Waverier, the schematics on cb tricks are not quite complete. i installed all new caps in amp. rewound rfc, new parasitic resistors,new bias resistors on 572's and new blocking cap.i have been working on tube amps for about 25 years, first mohawk that has caused so many problems. it was in very poor shape when i got it. figured great!, something to mess with..., boy, what a mess. i,m not perfect and there is'nt alot of info on the mohawks. input is allways taken to heart. this amp was given to me along with a black cat jb-12. thats for another day. thanks ,soretooth
Perhaps look at the tuned input to the driver stage, ( if it even has a tuned input) put a small antenna coupler between the radio and the amp, adjust it for minimum vswr on the input and see if this helps any.
Fixing up those old tubers are fun, I got shelves full of them, get them as junk and get bored fix them up then they sit there.
If it is anything like the Dentrons or the old hunter Bandits they are prone to oscillation on 10 and 15 meters. I found that 42 ohms of resistance bias on the grids seem to calm this down. The resistors need to be about 5 watts in the hunter bandit, you may be able to use a smaller value since the Mohawk is just two tubes. Good luck.
Fixing up those old tubers are fun, I got shelves full of them, get them as junk and get bored fix them up then they sit there.
If it is anything like the Dentrons or the old hunter Bandits they are prone to oscillation on 10 and 15 meters. I found that 42 ohms of resistance bias on the grids seem to calm this down. The resistors need to be about 5 watts in the hunter bandit, you may be able to use a smaller value since the Mohawk is just two tubes. Good luck.
it has a slug tuned input coil, i'll check the vswr. most golden screwdriver operators don't mess with them as they don't know the function,but it's possible. bias resistors are 49 ohm 5 watt and i replaced them when i recapped the amp just for gp. the part of the schematic that is missing is the voltage/ current selector switch and the input circuit board, both would be helpful.
tube amps are fun to work on, and i love the satisfaction when a repair is complete and the amp functions better or like new. started on this one because i finished my homebrew amp i now use. runs 2 3-400z's with 2 1000 watt microwave oven transformers in parrellel. 12- 650 mfd/ 450vdc computer grade caps for filter bank. drive it with homebrew 2- 6ju6 amp with a 1960 TV tranny. sorry to ramble, but i really enjoy tubes. thanks for the help, i have tons of stuff here if you need anything just ask.
tube amps are fun to work on, and i love the satisfaction when a repair is complete and the amp functions better or like new. started on this one because i finished my homebrew amp i now use. runs 2 3-400z's with 2 1000 watt microwave oven transformers in parrellel. 12- 650 mfd/ 450vdc computer grade caps for filter bank. drive it with homebrew 2- 6ju6 amp with a 1960 TV tranny. sorry to ramble, but i really enjoy tubes. thanks for the help, i have tons of stuff here if you need anything just ask.
Glad you got it going, what part of the circuit did you find the bad components in?
Reason I mentioned the input circuit is it is not unusual to find an amp that has been on 11 meters ( or other bands for that matter)to be over driven to the point of component failure.
Reason I mentioned the input circuit is it is not unusual to find an amp that has been on 11 meters ( or other bands for that matter)to be over driven to the point of component failure.
bad 25k 15 watt resistor open in the line voltage / driver power supply board. had a 30k and a 20k wirewound in junk box. went with the 30k for over kill.works great had to retune input very little. changed 2 47pf mica caps and 1 27 pf mica cap 5% + or -. put 1 50 pf and 1 47pf, and 1 33pf in place. all three +or- 5%. what i had and they worked. all of them on input board. what a pain to, relay is mounted to board and screwed to case. tuned for 1 hour to get it right. 1 watt input, 50 watt dead key, 600 watts on swing. dosey meter. contacts say it rocks. i love it when it talks right.
microwave tranny's in service for 4 months no problems at all. tell contacts it's my chicken cooker, coffee, lunch and dx all at the same time. He,He. easy to build and cheap to. going to run the mohawk for a week or two and then sell it. driver runs class ab and runs the finals class b. sweet amp. thanks very much for your help, getting old and forget simple stuff untill some one jogs my memory. again thanks alot, 73's. stay in touch. soretooth
microwave tranny's in service for 4 months no problems at all. tell contacts it's my chicken cooker, coffee, lunch and dx all at the same time. He,He. easy to build and cheap to. going to run the mohawk for a week or two and then sell it. driver runs class ab and runs the finals class b. sweet amp. thanks very much for your help, getting old and forget simple stuff untill some one jogs my memory. again thanks alot, 73's. stay in touch. soretooth
Sounds good and happy to see you got it working.
No B+ on the driver side? That 6146 was just a fancy conductor until you got that resistor fixed.
Idea if you want to consider modifying that old Mohawk. With such a small amount of RF producing that much of a carrier, maybe put a variable input resistor, sort of like Texas star did there amplifiers.
That way the op can control the dead key with the variable instead of trying to tune the radio to match the amp.
Just a suggestion.
I have been looking at those transformers for B+, nice and if in parallel looks like it would hold the current.
I have read somewhere where it is recommended to use 240 primaries transformers, with only 120vac input to provide more stability.
3-400Z, those old tubes have not been around for a while. Last pair I seen was in an Drake L4 which needed repaired, it ended up with upgrade on the PS and a pair of 3-500Z's in it.
No B+ on the driver side? That 6146 was just a fancy conductor until you got that resistor fixed.
Idea if you want to consider modifying that old Mohawk. With such a small amount of RF producing that much of a carrier, maybe put a variable input resistor, sort of like Texas star did there amplifiers.
That way the op can control the dead key with the variable instead of trying to tune the radio to match the amp.
Just a suggestion.
I have been looking at those transformers for B+, nice and if in parallel looks like it would hold the current.
I have read somewhere where it is recommended to use 240 primaries transformers, with only 120vac input to provide more stability.
3-400Z, those old tubes have not been around for a while. Last pair I seen was in an Drake L4 which needed repaired, it ended up with upgrade on the PS and a pair of 3-500Z's in it.
the variable resistor sounds like a good idea. the micro trannies run the 3-400z's great. i've had other people, even on this site mention core saturation and heat but it seems to get by. quess you could put them in oil. i remove the inner secondary from the core for safety reasons.( core would be at high voltage and need to be insulated from case. not to mention lethal.) watch the kind or tranny you use newer one have alluminum windings that are copper clad. work fine, but if you break the factory bonded connector off when you remove the inner sec wire from core, it will not solder back on.
. had 4 in series parrellel to start with, missmatched trannies but it was over kill, and a bit harder to wire.240 on primaries. worked fine too.
mine are alluminum wiring and when i solder a wire on the inner tab i removed from core i use 5 minute epoxy to glue it to the paper on top of tranny as it is very easy to break off. mine run on 115vac in parellel. temp wire the secondaries together and switch it on real fast, if it hums real loud swap sec wires. you could do it the low voltage test phasing way too. build your retifier and filter bank and ther you go. 2400vdc around 800 to 1000 ma.
. had 4 in series parrellel to start with, missmatched trannies but it was over kill, and a bit harder to wire.240 on primaries. worked fine too. mine are alluminum wiring and when i solder a wire on the inner tab i removed from core i use 5 minute epoxy to glue it to the paper on top of tranny as it is very easy to break off. mine run on 115vac in parellel. temp wire the secondaries together and switch it on real fast, if it hums real loud swap sec wires. you could do it the low voltage test phasing way too. build your retifier and filter bank and ther you go. 2400vdc around 800 to 1000 ma.
