I am having a problem with a Heathkit 201a it started out as on the back next to tubes a 28uh choke, 3300 ohm resistor and the .02 disc cap burned out I have replaced these. Now amp will put out watts with switch in grid position but when I switch to HV it will not make any. The HV position is where I was making all my high watts before. In grid keying up amp shows 300 on amp scale and when switched to HV 2300. I would like to get some ideas or input on this problem if possible please give me a direction. Thanks Jimbo165
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
Heathkit SB201a
- Thread starter Jimbo165
- Start date
Heathkit 201a
Wavrider I looked at schematic and see that switch is just for checking different values. I show 300 on grid and 2300 plate volts on SB200a meter I have a volt meter that only goes to 1500v and when I check voltage at top of tubes it pegs my meter I am in process of getting a volt meter that will have a higher volt testing but it has not arrived yet. My swr is 1.2 and I am not having any problems running my other amps through my setup so no problem there. The switch should not make a difference but it has on out put watts on my watt meter for some reason. Another thing is tubes cherry some when keyed up but put out some watts in grid but not when switch is in HV mode. Could there be a problem with keying circuit?
Wavrider I looked at schematic and see that switch is just for checking different values. I show 300 on grid and 2300 plate volts on SB200a meter I have a volt meter that only goes to 1500v and when I check voltage at top of tubes it pegs my meter I am in process of getting a volt meter that will have a higher volt testing but it has not arrived yet. My swr is 1.2 and I am not having any problems running my other amps through my setup so no problem there. The switch should not make a difference but it has on out put watts on my watt meter for some reason. Another thing is tubes cherry some when keyed up but put out some watts in grid but not when switch is in HV mode. Could there be a problem with keying circuit?
Last edited:
Honestly I do not know where to start at. without the amp sitting in front of me to do some resistance and continuity checks.
It does seem like you have plenty of HV.
The VSWR is the INPUT to the amplifier, hopefully you are tuning it into a dummy load.
you still did not mention any band. What frequency are you testing this amp at?
300ma grid is excessive.
tubes will turn red if mis tuned or driven to hard.
I would look at the metering circuit to make sure all is working as it should.
you have the schematic, that is good.
Make sure the amp is unplugged and the HV is bleed off. then start looking at metering circuits. compare to your schematic and see what if any components are bad .
the keying circuit is simple in that amp, schematic will show it.
the grid resistors are known to change values under excessive stress, heat or just time you may want to look at them also.
It does seem like you have plenty of HV.
The VSWR is the INPUT to the amplifier, hopefully you are tuning it into a dummy load.
you still did not mention any band. What frequency are you testing this amp at?
300ma grid is excessive.
tubes will turn red if mis tuned or driven to hard.
I would look at the metering circuit to make sure all is working as it should.
you have the schematic, that is good.
Make sure the amp is unplugged and the HV is bleed off. then start looking at metering circuits. compare to your schematic and see what if any components are bad .
the keying circuit is simple in that amp, schematic will show it.
the grid resistors are known to change values under excessive stress, heat or just time you may want to look at them also.
Heathkit
Thanks so much for your help. I found problem it was a 1.5 resistor on what looks like a keying type circuit it looked ok looking down on it but back side was burned. I replaced it and ma now 100 to 120 and it works fantastic getting close to 1000 pep with 811 tubes all together I had to replace 3 resistors a 28uh choke and a disc capacitor. It has been a learning experience for sure this bias type keying amps are different. Thanks Again.
Thanks so much for your help. I found problem it was a 1.5 resistor on what looks like a keying type circuit it looked ok looking down on it but back side was burned. I replaced it and ma now 100 to 120 and it works fantastic getting close to 1000 pep with 811 tubes all together I had to replace 3 resistors a 28uh choke and a disc capacitor. It has been a learning experience for sure this bias type keying amps are different. Thanks Again.
BJ radionut
Supporting Member and 6m addict
Please don't tag me as rude...
However 120ma of Grid current is much to high for a pair of 811a's....
50-60ma would be considered about right
That's borderline for a pair of 572b's....(which is the proper tube for that amplifier)
Again don't take this wrong but even with 2300v as B+...a pair of 811a's are (or should be) more like 500 watts max...
Todays 811a's should have MAX 2000v....More like 1500-1700v
One of my amps runs (3) 572b's at 1850v B+....
Output 700 watts Peak!...on SSB with 50 watts drive....
Avg.grid current 60ma
Unless you have and endless supply of RCA or Raytheon(JAN)811a tubes...
You better crank it back!!!!!
One more thing....You might need a better wattmeter...that one is telling a fib
All the Best
BJ
However 120ma of Grid current is much to high for a pair of 811a's....
50-60ma would be considered about right
That's borderline for a pair of 572b's....(which is the proper tube for that amplifier)
Again don't take this wrong but even with 2300v as B+...a pair of 811a's are (or should be) more like 500 watts max...
Todays 811a's should have MAX 2000v....More like 1500-1700v
One of my amps runs (3) 572b's at 1850v B+....
Output 700 watts Peak!...on SSB with 50 watts drive....
Avg.grid current 60ma
Unless you have and endless supply of RCA or Raytheon(JAN)811a tubes...
You better crank it back!!!!!
One more thing....You might need a better wattmeter...that one is telling a fib
All the Best
BJ
Heathkit 201a
I will look into dropping ma down all I have to do is change resistor value but amp is working fantastic and as far as pep I know this 1000 pep can be off but I did check it with 3 separate meters and all said same value. We have a friend running same amp and his HV is like ours in 2300 to 2400 value and he has run amp for at least 8 to 10 years with no problem. We also then used a Firebird F500 amp to drive Heathkit Pep and avg was impressive, talking to contacts in our area asking for Db readings and changes showed us that this amp is doing very very well. We are not using Firebird again have put a JB 150b to drive it now and if it goes up in smoke I guess I will just keep the American economy going by buying parts and repair it again. 572 tubes will be in next week so we will see what kind of pep output we will have then and will look into getting a watt meter that will tell us exact output so next time I can give you a true pep. Regardless I do want to thank you all for your input good ,bad or whatever this is a great forum and being new to I have so much to learn and please ask for your patience. Jimbo165
I will look into dropping ma down all I have to do is change resistor value but amp is working fantastic and as far as pep I know this 1000 pep can be off but I did check it with 3 separate meters and all said same value. We have a friend running same amp and his HV is like ours in 2300 to 2400 value and he has run amp for at least 8 to 10 years with no problem. We also then used a Firebird F500 amp to drive Heathkit Pep and avg was impressive, talking to contacts in our area asking for Db readings and changes showed us that this amp is doing very very well. We are not using Firebird again have put a JB 150b to drive it now and if it goes up in smoke I guess I will just keep the American economy going by buying parts and repair it again. 572 tubes will be in next week so we will see what kind of pep output we will have then and will look into getting a watt meter that will tell us exact output so next time I can give you a true pep. Regardless I do want to thank you all for your input good ,bad or whatever this is a great forum and being new to I have so much to learn and please ask for your patience. Jimbo165
Last edited:
SB201a
Wavrider & BJradionut you were right about ma and tuning of amp it was giving us plenty of pep and watts but tubes were taking a beating trying to get more out of amp than it should produce I changed resistor value and brought ma down to under 100. We installed the 572b tubes retuned it and now do not have problem with tubes getting cherry and amp still working great. I have looked at pictures of other 200 and 201 amps on internet and found that alot of the resistor and capacitors are of different values than on cb tricks schematic of amp some seem to be quite a change in values is there a reason for this? Just for some info this amp is not mine and not treated this way by me. I may get one for myself someday but right now I have other amp interest.
Amp belongs to my brother . Thank You all again and I hope to keep learning with your help.
Wavrider & BJradionut you were right about ma and tuning of amp it was giving us plenty of pep and watts but tubes were taking a beating trying to get more out of amp than it should produce I changed resistor value and brought ma down to under 100. We installed the 572b tubes retuned it and now do not have problem with tubes getting cherry and amp still working great. I have looked at pictures of other 200 and 201 amps on internet and found that alot of the resistor and capacitors are of different values than on cb tricks schematic of amp some seem to be quite a change in values is there a reason for this? Just for some info this amp is not mine and not treated this way by me. I may get one for myself someday but right now I have other amp interest.
Amp belongs to my brother . Thank You all again and I hope to keep learning with your help.
Last edited:
CBers and happy watt meters go hand in hand like apple pie and baseball. lol
When he said 1000 watts out of that amp with 811A's in it at 2300 volts I almost crapped myself. Those tubes should be inspected for burn holes as I know they must have some.
If the anodes don't have holes in them I bet they are caving into the grids. With each key at 2300 volts the anodes will melt a little more and bend in towards the grids until one day they arc. The symptom here will be the 33 ohm resistors, RF bypass caps and meter shunt resistor will all blow up in the amplifier grid circuit. I think there is even a choke inline with the grid that can burn open. Sounds like the problem has already happened once. Also, changing the value of the grid meter shunt that burned open has little effect on actual grid current and much more effect on the calibration of the meter.
PS: When working on equipment such as this, always remember that 2300 volts is 300 volts more than they use with the electric chair!
PS: When working on equipment such as this, always remember that 2300 volts is 300 volts more than they use with the electric chair!
It is never a good idea to hot rod these amplifiers. They were never ment to be pushed that hard.
A good rule of thumb if you want reliable service and want solid power is to have a big enough amplifier and run it WAY below it's specs and it will last a lifetime with minimal maintinance.