AL-811H problem/ question

[Crambone]

I acquired an AL-811H from a friend but he said it had some issues so I did the following. Its wired for 220 so first thing I did was check to see if wired properly and check fuse values, all good. I pulled the tubes and tested continuity between pins and found one with a filament to grid short. I pulled the tube sub chassis out and found the grids are wired directly and it looks proper. I ordered 4 new 811A Pent Lab tubes to be on the safe side. I cleaned all the switches, contacts… and re-assembled. I left the tubes out and brought up on my 120v variac and all voltages checked good and no smoke! So I powered off and plugged into 220 and fired up again with tubes in and let sit for 1hr in Standby, checked all voltages …. And all good. I then tuned up on 40 Meters AM at 10 watts and looked good so slowly brought up power to 50 watts and HV is 1750 and Plate is good but grid meter pins?
im not sure what’s causing Grid Meter to pin anything I can check?

KB2LMN

 

[338_MtRushmore]

12.) Grid meter pins with low drive power

• No plate current
  • Open RF plate choke or no high voltage
• Low plate current that does not change with tuning
  • Open tank circuit feed, open blocking capacitor
• Normal plate current and output, but grid meter pins hard
  • Open grid shunt R8 1.5 ohm
    • Can be caused by filament to grid/ground short or tube forced in socket wrong
• Low RF power output
  • Loading control too far meshed, load capacitor shorted, or antenna system bad
• Also see 1 and 2

Ameritron AL80B AL811H AL572 Amplifier Trouble Shooting

 

[BayouRadioAmplifier]

I got one of them. have melted 811 plates. popping the AC input fuses.
popped some of the resistors in line with the grids. etc.
(yes, I need to ground the grids directly some day!)
.
but a friend sent me some old Russian made 811's and
it has been working great since then!
.
make sure your LOAD control knob at position 10 has that variable
capacitor about fully opened. lowest capacitance.
.
put the LOAD control at 5. drive the amplifier with about 15 watts or so,
and peak with the TUNE control. notice the output power level.
then turn the LOAD to 4.5 or so and retune. check for more power
output. and go down some more, until you have about 10 dB gain.
15 watts in for about 150 watts out. check grid current.
this will get you close to proper tuning. then go to about 70
watts in for 700 watts output. do this real quickly.
give the tubes a rest. it is good to turn the LOAD control
back to a higher setting, higher number, (clockwise)
less gain, and a lower impedance at the plates, less voltage
there, less chance of arcing. and always the TUNE control
to peak it up, last.
.
on my 811H the LOAD is usually around 3 to 4 on all bands.
peak with the TUNE last... yes, tune with the TUNE control last.
works fine. I peg the grid meter a little in SSB mode.
.

 

[mechteacher]

Ameritron AL-811 amp.
Connected RF in to RF OUT, placed to on and into XMT OPR, Then was trying to tune the amp, Grid and Plate both spiked. After finding the error of the connection that caused Grid current to spike momentarily, the amp failed to operate.
This amp has TOF-2 installed. TPS3 and 811KP Arc Protection kit have been installed and were all working prior to this problem. I have a power/SWR meter connected at the amp output.
1. new tubes installed did not correct operation.
2. cleaned both wafer switches per CTR Engineering's recommendations.
3. Replaced C8&9 with no change in operation.
Power on, HV = 1.8 KV STBY on, Grid = zero Exciter 40 watts Plate = zero Ip = zero
Band 20/30, Load 4 ½, Plate = 8 ½ SWR = 1.07, Plate current = 100ma Grid = zero
Exciter was increased to 70 watts with no change.
Power out to antenna zero with amp in XMT OPR
Exciter shows SW infinity.
Power out to antenna 70 watts with amp in STBY
Exciter shows 1.+ SWR and 70 watts out put.
Checked Relay continuity from RF Out PL239 to the tube sockets filament connection.
Plate Choke, L4, continuity from clamp at base to tube caps checked good.
Checked Relay continuity from RF IN, PL239 through the relay to the two Capacitors, C8&9. It stops there.
Continuity check of the Filament Choke, L2

Capacitors C15, C16, C17, C18, all checked good, as well as the all the diodes and both fuses.

 

[mechteacher]

Here is the AL-811 Schematic

 

[Dr. Frankenstein]

@ mechteacher

Have you checked D6 (1N4007) and R9.

R9 is B- to the center tap to the Filament Transformer that puts voltage to the tubes,
without the voltage to the tubes the radio's RF has no place to go.

73

 

[mechteacher]

@ mechteacher

Have you checked D6 (1N4007) and R9.

R9 is B- to the center tap to the Filament Transformer that puts voltage to the tubes,
without the voltage to the tubes the radio's RF has no place to go.

73

Dr. Frankenstein,

Thank you very much for looking at my problem. Here is what I just verified.
I rechecked D4-15 and R 8,9,10,11 all checked good.
Checked AC from transformer at the diode board, 1260 VAC. That was with tubes installed and no RF, amp pwr on, STBY switch in OPR.

What next would you suggest?

Mechteacher

 

[Dr. Frankenstein]

Have you checked for filament voltage at "L2" where "C8" & "C9" meet at "L2"?

 

[nomadradio]

Sure makes it sound like there's a 'glitch' resistor that's popped in line with the HV to the anode choke. A DC meter that can safely handle 2000 Volts DC to the plate cap of a tube would reveal this if it's the problem. Zero Volts on the tube plates will get you a pegged-out grid meter. Might explain the "POP".

73

 

[mechteacher]

Have you checked for filament voltage at "L2" where "C8" & "C9" meet at "L2"?

Tube plates are powered. Checked voltage at L2, (J3 RLY shorted) found 9.3 vac in stby and 3.2 vac in opr (S3 closed, & RelayRL1 closed).
Continuity checked good, manual actuation to relayRL1 between FR IN (J2) to C8&9.

Thank you again for the help.

 

[mechteacher]

I may have found the problem. C13 Capacitor from the parasitic suppressor to the air coil. I read it as 220 pF, not the 1000 pF rated.
Parts on order.
Thank you for looking at this for me.
I will update when part is installed.

 

[linearone]

Sure makes it sound like there's a 'glitch' resistor that's popped in line with the HV to the anode choke. A DC meter that can safely handle 2000 Volts DC to the plate cap of a tube would reveal this if it's the problem. Zero Volts on the tube plates will get you a pegged-out grid meter. Might explain the "POP".

73

I have a very specific opinion on "glitch" resistors. 99% of people install a resistor on the b+ and think they did something. If the b+ isn't fused before the glitch resistor than the resistor becomes a slow blow fuse. I'd rather use a fast acting fuse and use the resistor to limit the current. I just feel like a glitch without a b+ resistor is kinda silly.

In a perfect world, all amps would have hv secondary fuses before the rectifiers, a b+ fuse, a b+ glitch resistor, a cathode fuse, and a grid trip circuit that would shut it all down if you pull too much grid current . If we all did that it would make for a pretty Stout box.

 

[mechteacher]

I have a very specific opinion on "glitch" resistors. 99% of people install a resistor on the b+ and think they did something. If the b+ isn't fused before the glitch resistor than the resistor becomes a slow blow fuse. I'd rather use a fast acting fuse and use the resistor to limit the current. I just feel like a glitch without a b+ resistor is kinda silly.

In a perfect world, all amps would have hv secondary fuses before the rectifiers, a b+ fuse, a b+ glitch resistor, a cathode fuse, and a grid trip circuit that would shut it all down if you pull too much grid current . If we all did that it would make for a pretty Stout box.

Thank you very much for the input. I will continue checking and making updates here to keep everyone informed.

79 --... ...--
Bob K9HOU

 

[linearone]

Thank you very much for the input. I will continue checking and making updates here to keep everyone informed.

79 --... ...--
Bob K9HOU

I'm sorry, that became more an essay on amplifier building than a helpful comment on an Ameritron. I apologize.