|
What I think Lou is saying is...... the cut off bias isn't being applied on RX....( cuz of lousy bias relay contacts on RX)...... hence the tubeS are sucking normal idle current.? BUT if that was the case, the plate current meter would be indicating normal idle current.? ?Now that the amp seems to be functioning ok...... what is the normal idle current ????? (keyed, but NO drive applied).?
?
With normal idle current, how much idle current is there...and what is the loaded B+?? ?Knowing that, simple calc to determine idle anode dissipation.?
|
One picture clearly shows the the CT bias resistor and the zener diode being switched by a relay (blue)mounted on the center wall. ?The PC board which looks like a relocation of the ALO board might be doing some detecting of swr or something that might shut down??the ptt? or something. ?Bug it sure doesn’t look transistor bias switching with the wiring I see over to the blue relay. He’s got a radio Dan?gizmo with a coax going onto it. ?I’m wondering if that senses RF and triggers the relay PTT line, ? This is definitely one for my memoirs. ?Just when you thought you’ve seen it all something comes along and takes the cake. ?Engineers build?amplifiers and hams cone along and try to make it better. I could fill up a 55 gallon drum of modifications I ripped out of amps. ?With no documentation it gets costly to spend the time to figure out what some?? screwdriver happy ham had in his brain. Jeez
On Friday, December 1, 2023, 12:39 AM, John Roland <johnroland51@...> wrote:
|
Adrian and all
I measured the voltage across what I believe to be R6 in the 1988 power supply schematic or R1 in the 1983 schematic.? It is visible in the 4th picture I sent yesterday evening (PST) in the upper right corner of the 4th picture down as a large 100k resistor attached to the large zener diode.
? I hooked up my tranceiver output to the dummy load but left the relay connected to the amplifier and keyed and unkeyed the transceiver in RTTY mode.? Amp in XMT mode.?? Transmitter unkeyed, the voltage across the resistor was around 44.5 volts.?? Keyed, the voltage was a few millivolts.??
Someone asked about idling current.? With no drive but the amp keyed I'm seeing about 80 ma? plate current and about 30 ma grid current.? Both meters drop to 0 when unkeyed.
XYL insists I clear the 300 foot driveway of the foot of snow that fell last night so I'll be away for the next few hours.
/John
|
The clue is surely in the grid current reading. It should be zero with no drive.
73, Alek VK6APK.
toggle quoted message
Show quoted text
On 2/12/2023 5:49 am, Adrian Fewster wrote: I had asked for that. what is the same result for each tube on its own with the other removed ?
Also voltage across zener keyed and unkeyed ?
73
vk4tux
On 2/12/23 06:47, John Roland wrote:
Someone asked about idling current.? With no drive but the amp keyed I'm seeing about 80 ma? plate current and about 30 ma grid current.? Both meters drop to 0 when unkeyed.
|
Adrian and all
I sent a similar reply a few hours ago, but it doesn't show up, I assume it's lost.? And if not I hope the 2 versions are consistent.
I measured the voltage across the 2 terminals of the big zener.
? key down 9.3 volts
? key up? 9.1 volts
Individual Tube Idling Currents Keyed, no input signal
Rear Tube:? Plate: 40 ma? Grid 10 ma
Front Tube Plate; 60 ma??? Grid: 18 ma
All readings drop to 0 when unkeyed.
Cheers ? /John
|
You should not be getting any grid current reading.
Alek, VK6APK.
On 3/12/2023 6:11 am, John Roland
wrote:
toggle quoted message
Show quoted text
Adrian and all
I sent a similar reply a few hours ago, but it doesn't show up, I
assume it's lost.? And if not I hope the 2 versions are
consistent.
I measured the voltage across the 2 terminals of the big zener.
? key down 9.3 volts
? key up? 9.1 volts
Individual Tube Idling Currents Keyed, no input signal
Rear Tube:? Plate: 40 ma? Grid 10 ma
Front Tube Plate; 60 ma??? Grid: 18 ma
All readings drop to 0 when unkeyed.
Cheers ? /John
|
I use? 10 x 1N5408 diodes in series for aprx 7.2 vdc bias on my drake amps ( 2 x 3-500Z's)...... and they are 2650 vdc on RX.? Idle is then 100 ma.? ?(and just 40 ma on the lower CW / 1900 vdc mode).?
Imd is superb in either position. ( 1290 watts pep out with 2.5 kv loaded............. and 625 watts pep out with 1850 vdc loaded).?
?
BUT he should have NO grid current at all, when keyed, and no drive applied.? Something is still amiss.??
|
On 12/3/2023 7:44 AM, Jim VE7RF wrote:
BUT he should have NO grid current at all, when keyed, and no drive applied.? Something is still amiss.
Considering the condition of that modified amp, I wonder if perhaps the grid current circuitry is miswired, and has always indicated something, but the operator just didn't realize it wasn't reading correctly until the troubles began and we began asking questions about what he was seeing?? With wires running every-which-way, it looks like a mess, in those pix. And BTW, someone please remind me what problem suddenly reared its ugly head to bring the owner-operator here for help, in the first place?? Steve, K0XP
|
It’s hard to know what someone did there. ?It’s a mess. ?If the B- has a safety diode somewhere and it’s shorted the grid meter will respond in kind with the plate meter ( a la Ameritron) the grid meter is NOT seeing grid current is basically in parallel with the plate meter and responds on kind. ?The OP showed a photo which appeared thT the two meters were exactly above zero the same amount in idle.
On Sunday, December 3, 2023, 10:58 AM, Steve <k0xp@...> wrote: On 12/3/2023 7:44 AM, Jim VE7RF wrote:
>
> BUT he should have NO grid current at all, when keyed, and no drive
> applied.? Something is still amiss.
>
Considering the condition of that modified amp, I wonder if perhaps the
grid current circuitry is miswired, and has always indicated something,
but the operator just didn't realize it wasn't reading correctly until
the troubles began and we began asking questions about what he was
seeing?? With wires running every-which-way, it looks like a mess, in
those pix.
And BTW, someone please remind me what problem suddenly reared its ugly
head to bring the owner-operator here for help, in the first place??
Steve, K0XP
|
?
That might be caused by a short from B- to ground (safety diode?).?
In that case anode current is measured via the grid current shunt resistor and shown as grid current as well.
?
73
Peter, DJ7WW
?
?
?
?
-----Original-Nachricht-----
Betreff: Re: [ham-amplifiers] Need Help with Amp Supply LK500ZC
Datum: 2023-12-03T16:45:06+0100
Von: "Jim VE7RF" <jim.thom@...>
?
?
BUT he should have NO grid current at all, when keyed, and no drive applied.? Something is still amiss.??
?
|
Happy New Years Everyone,
?
Its that time of year when I'm spending more time in the shack and am back looking at the LK-500 ZC.? In response to the many (much appreciated ) suggestions that I could deal with, I replaced the two little blue relays: one bypasses the cut-off resistor, and the other energizes the antenna relays.?? Unfortunately, this changed nothing.?
I also put a request on three of my regional (Portland, Columbia River Gorge and Bellingham) ARC reflectors looking for someone willing to test my tubes in their amplifier and the only replies I got was from people candidly saying they wouldn't take a chance on damaging their amps with my dubious tubes.?
?
I'm thinking if there is a tube defect, it seems unlikely both tubes would be defective.?? Could I test that by removing each tube and seeing if the overheating results when each tube is operated individually?? And would running a single tube risk further damage to the? amplifier?
?
To refresh your memory of this issue, the amp will (usually) idle with no issues, but when more than 10 watts of exciter power is applied, both tubes begin to glow red. The front tube seems to lead the rear tube.
?
Thanks /John W7SWB
?
|
I believe Econco will function test transmitting tubes.
You might check with W8JI, too.
?
Hal Mandel
W4HBM
|
John,
?
It could be a cold solder joint in a tube pin.
?
If it was an interelectrode short, you could use a DMM
to explore.
?
If it was a defective plate blocker it would
show up with a meter, out of the circuit.
?
You can run 1 tube at a time, no problem,
and do each separately from each socket.
?
If there was a bypass cap short this might also
be seen, as the bypass circuit will mess up on
both tubes at the same time, but only on one socket
at a time. Again, use a DMM to trace.
?
When you run 1 tube at a time, note the ammeter
readings at 1 watt, 5 watts, 10 watts, etc., and
compare.
?
Hal W4HBM
|
Hal and all,
I've started testing each tube in each socket individually and will post my results hopefully later today.? The first tube doesn't show any shorts with a DMM.? I don't know what a "plate blocker" is.? Thanks for the help.?? /John
|
Plate Blocker is the big capacitor that is connected to the plate tune capacitor coming off the tube anode. Should be 5kv or more rated. Shorts won't always show with a multi meter till they get warm.
[Edited Message Follows]
Hal and all,
I've started testing each tube in each socket individually and will post my results hopefully later today.? The first tube doesn't show any shorts with a DMM.? I don't know what a "plate blocker" is.? Thanks for the help.?? /John
|
That helps,? I was thinking maybe he meant the plate choke.
Thanks
On Thu, Jan 2, 2025, 11:46?AM mike repinski via <mikflathead= [email protected]> wrote:
Plate Blocker is the big capacitor that is connected to the plate tune capacitor coming off the tube anode. Should be 5kv or more rated. Shorts won't always show with a multi meter till they get warm.
On Thursday, January 2, 2025 at 11:44:33 AM EST, John Roland via <johnroland51= [email protected]> wrote:
[Edited Message Follows]
Hal and all,
I've started testing each tube in each socket individually and will post my results hopefully later today.? The first tube doesn't show any shorts with a DMM.? I don't know what a "plate blocker" is.? Thanks for the help.?? /John
|
Just letting you know,?
Effective? Nov 2024 ECONCO no longer tests tubes at no charge.
The fee is now $150 per tube.
thanks to the new corporate owner TransDigm.
?
Reid??
?
Re: Need Help with Amp Supply LK500ZC
? Date: Wed, 01 Jan 2025 11:27:50 PST
?
I believe Econco will function test transmitting tubes.
You might check with W8JI, too.
?
Hal Mandel
W4HBM
|
Hi Everyone,
I thought I might find a bad tube by swapping both tubes in and out one at a time.?? Only thing I confirmed is that what ever the problem is, it hasn't healed itself.?? FWIW I checked both tubes with a DMM and found no evidence of any shorts.? Below is the results of my testing.? I am probably done with this kind of testing as the SWR spikes make me fear for my transceiver. ? I'll be away from this for a while, but reading about grounded grid amps in my spare time, but if you see any clues here, please share.??
73?? John W7SWB
?
?
| Socket |
Tube? |
Watts In |
Plate I |
Grid I |
Watts Out |
? |
| Rear |
Rear |
0 |
40 |
10 |
? |
? |
| Rear |
Rear |
0.7 |
50 |
18 |
9 |
? |
| Rear |
Rear |
9.8 |
130 |
40 |
90 |
? |
| Rear |
Rear |
20 |
180 |
60 |
100 |
? |
| Rear |
Rear |
30 |
180 |
60 |
170 |
After key down Starts to glow and output power drops |
| Front |
Rear |
0 |
40 |
10 |
? |
? |
| Front |
Rear |
0.7 |
60 |
20 |
10 |
? |
| Front |
Rear |
9.8 |
140 |
45 |
80 |
? |
| Front |
Rear |
20 |
200 |
60 |
170 |
Starts to glow when keyed but fades key up.? High SWR on Transceiver |
| Front |
Front |
0 |
? |
? |
? |
? |
| Front |
Front |
0.7 |
? |
? |
? |
? |
| Front |
Front |
9.8 |
? |
? |
? |
? |
| Front |
Front |
20 |
200 |
70 |
170 |
Started to glow red and power dropped? SWR pegged for an instant on keyup.? 2 hours later tube glowed immediately and SWR spiked.? |
| Front |
Front |
30 |
? |
? |
? |
? |
| Rear |
Front |
0 |
? |
? |
? |
? |
| Rear |
Front |
0.7 |
? |
? |
? |
? |
| Rear |
Front |
9.8 |
? |
? |
? |
? |
| Rear |
Front |
20 |
240 |
80 |
250 |
After key down, starts to glow red and power drops. |
| Rear |
Front |
30 |
? |
? |
? |
? |
| ? |
? |
? |
? |
? |
? |
? |
| Transmitter repeatedly keyed in RTTY mode for 5 count |
? |
| Watts in measured with MFJ 993B |
? |
? |
? |
| Watts out measured with Heathkit HM-2140 (ballpark) |
? |
| IC-7300 Output Set |
0% |
11% |
25% |
33% |
? |
? |
| Watts out |
0.7 |
9.8 |
20 |
30 |
? |
? |
| ? |
? |
? |
? |
? |
? |
? |
?
|
HaL Mandel
Brandon DX