I¡¯m working on a used AL-811 for a friend. The 811 tubes were bad, so I replaced them with some Penta Labs 572b tubes (A whole another adventure). I also replaced the tube
sockets, and installed GDTs on the tube sockets and added some bias diodes on the center tap of the transformer. I made sure there were not MOVs in the input board. The issue I¡¯m having is high SWR (over 2:1) on 80 meters and I can¡¯t get full drive from what
appears as the exciter is folding back. All the other bands are fine.
?
I¡¯ve attempted to adjust the 80-meter input coil with no effect on SWR/PWR in. I¡¯ve checked the input switch for continuity and from the input through the 80-meter input coil
with no problems. Switch alignment looks good. I remove and tested C4 (for 80 Meters) a 500pF cap and it tested good. ?I¡¯ve removed the 200-ohm padding resistor just to see what effect it had on SWR and nothing. Obviously, I get more output for the same amount
of drive. If I¡¯m at the high end of 75 meter with the tuning slug all the way at the end of the coil form, the SWR just starts to drop, and I see an improvement in drive level. With the padding resistor in circuit, I¡¯m showing about 50 watts for drive and
60mA of grid current. With the amp in bypass the radio will do 120W no SWR.
?
I¡¯m wondering about values of C4 and if anyone else has experienced this behavior after swapping to 572b tubes? Don¡¯t know how the amp performed prior as the tube replacement.
?
Thanks for any productive comments in advance.
?
Jim ¨C AA7CL
?
|
Vernier Drive Replacement - Ameritron AL series amp
Hello,
?
Has anyone had to replace the vernier drive on the load control of any of the Ameritron AL series amplifiers?
?
Thanks & 73,
Garry - K4OR
|
Ahh yes.? Aerotron used the 5894 in their base stations along with
the 6360 in their "lunch boxes".? IIRC, somewhere along the line
they used the 8643 also.
Andy? K9ATX
On 4/30/2025 8:34 AM, Mahlon Haunschild
- N4ZK via groups.io wrote:
Amperex had roughly half a dozen of these
push-pull tetrode types in their product line back in the day,
probably all targeted for the VHF/UHF land mobile radio
services.? All were single-ended input, push-pull output.?
Amperex even ran a full-page ad in the ham radio magazines /
handbooks for them.
The most famous of these (if you can call such a
thing famous) was the 5894, which was the tube used in the 100
watt PA in the Motorola Motracs.? I had a 10-watt Motorola
Business/Dispatcher that used the 6360 as a PA.
Best regards
Mahlon - N4ZK
"
The comment in the blurb
about frequent replacement
of the tetrode finals
make me wonder if the designers
were Tetrode Men."
?
Yes, it's easy to imagine
that development lab had some "politics" that impacted
the overall design ;-)
?
?
--
"Where the Old Soo crossed the New Soo"
Duplainville, Wisconsin
Broadcastify Train Scanner:
Youtube Channel:
|
Amperex had a tube lineup, mostly 9 and 11 pin receiving
miniatures that were serviceable, but they were out of
their league when pushing RF Power.
?
(For a minute I confused ¡°Amperex¡± with ¡°Ampex,¡±
who did make a quite decent set of reel-to-reel
multichannel analog audio recorders.) Ha, ha.
?
Hal Mandel W4HBM
|
Amperex had roughly half a dozen of these push-pull tetrode types in their product line back in the day, probably all targeted for the VHF/UHF land mobile radio services.? All were single-ended input, push-pull output.? Amperex even ran a full-page ad in the ham radio magazines / handbooks for them.
The most famous of these (if you can call such a thing famous) was the 5894, which was the tube used in the 100 watt PA in the Motorola Motracs.? I had a 10-watt Motorola Business/Dispatcher that used the 6360 as a PA.
Best regards
Mahlon - N4ZK
"
The comment in the blurb about frequent replacement
of the tetrode finals make me wonder if the designers
were Tetrode Men."
?
Yes, it's easy to imagine that development lab had some "politics" that impacted the overall design ;-)
?
?
|
"
The comment in the blurb about frequent replacement
of the tetrode finals make me wonder if the designers
were Tetrode Men."
?
Yes, it's easy to imagine that development lab had some "politics" that impacted the overall design ;-)
?
?
|
Tuesday, April 29, 2025; 0944EDT (UTC-5)
?
Dear Tim,
?
The comment in the blurb about frequent replacement
of the tetrode finals make me wonder if the designers
were Tetrode Men.
?
I¡¯m struggling with getting a GU-84b two-holer to the
point where I can put the key down on 10m, and the
most valuable asset was to include a GM3SEK
Tetrode Controller in the lineup.? The 2 ¡®84b¡¯s were
received N.I.B., but that doesn¡¯t stop a foolish move
from turning them to toast-in-a-heartbeat.
?
Hal Mandel W4HBM
|
Tuesday (Mardi),29 April 2025; 0940 EDT (UTC-5)
?
Dear Francois,
?
An excellent piece of research!
?
¡°C¡¯est un fabrication ancienne...¡±
?
Your comments are so well received here.
?
Hal Mandel
W4HBM
?
|
Seems very likely the site used this Pye T30AM/FM set in the 1960's 1970's. They used QQE0312 final stage and the former Pye engineers forum says these were well known for needing final tube replacement.
?
|
Re: Drake L7 [2 x 3-500Z] power ?
drive it till you get 500-600 ma...using the lower B+? ?(CW) position.? ?Then you will get your desired PO.?
?
|
Re: Drake L7 [2 x 3-500Z] power ?
1770 vdc loaded @ 565 ma = 1 kw DC input = 625 watts output.? ?600 watts out on upper HF freqs like 15+10m.?
|
The RFparts pictures show 6360 Its an equivalent of -- F1AMM Fran?ois
|
I think you've nailed it :-)
?
The RFparts pictures show 6360's have very distinctive internal structure matching my pictures
?
Many thanks
Tim
?
|
Re: Drake L7 [2 x 3-500Z] power ?
His problem is he's using the WRONG B+ position.? ? He should be using the lower? 1900 vdc ( CW position).? ?That will give him an easy 600+ watts pep out on ssb? / 600+ watts? CW / Data /? FT-8. just 40 ma idle on lower 1900 vdc position.? ?IMD is superb with [¡] ?625 watts pep out on the lower 1900 vdc position.? ? Can you tell me the corresponding input power? -- F1AMM Fran?ois De la part de Jim VE7RF via groups.io
·¡²Ô±¹´Ç²â¨¦?: mardi 29 avril 2025 07:07
|
Re: Drake L7 [2 x 3-500Z] power ?
On Mon, Apr 28, 2025 at 12:06 PM, Louis Parascondola wrote:
>You don¡¯t want less than about 160ma idle current for SSB and no less than about 100ma for CW or else it will require a lot of drive to get the amp up to a decent output. ?You can drive those tubes to
>A maximum of 900ma. Of plate current and a maximum of around 300ma. Grid current in ICAS. ?This should give you on excess off about 1300watt key down carrier. ?It will require between 80-100 watts of drive. ?If you >have a good set of tubes. ?Make sure you don¡¯t have too much operating bias. ?You shouldn¡¯t need mor than around 5-7v. ?I¡¯m working on a pair of L7 amps right now and will be testing them today.
Nonsense.? ?I use 10 x 1N5408's in series for bias. ( aprx 7.2 vdc) .? Idle is 100 ma on? 2650 vdc position............? and just 40 ma idle on lower 1900 vdc position.? ?IMD is superb with either 1290 watts pep out on 80m ( 800 ma? plate current + 300 ma grid current)? or? ?625 watts pep out on the lower 1900 vdc position.? ( 565 ma plate current....and I forget the grid current).? ?Dead easy to drive in either position.? His problem is he's using the WRONG B+ position.? ? He should be using the lower? 1900 vdc ( CW position).? ?That will give him an easy 600+ watts pep out on ssb? / 600+ watts? CW / Data /? FT-8.? With just 400 watts using the 2650 vdc position, the load control will be maxed out.? ?Running 400-500 watts out while using the 2650 vdc position will result in real low plate current.? ?The plate load Z? will skyrocket, and? the tank Q? will also skyrocket, like? by a factor of 2.7? times.? ? With 2450 vdc @ 310 ma, your plate load Z is now? 4750 ohms.? And the tank Q is now 27.? Eff will go to hell.? Properly operated at either? 565 ma @ 1770 vdc? ?or? 800 ma? @ 2500 vdc, the plate load Z is? ?1736 ohms.? ?The tank circuit in the L4B / L7 is designed for 1736 ohms , NOT 4750 ohms.? Francois? ?forget about the gain of the amp.? ? All of these? GG triode tubes amps will always exhibit far more? gain when driven with very low power, they all do.? And no, the tank eff will not improve as you go higher in freq, just the opposite.? ?Do all your testing on 40m.? Jim? VE7RF
|
Re: Drake L7 [2 x 3-500Z] power ?
Answers to various questions ? This is an amplifier I bought that had seen little use. When I baked the tubes as a precaution to degas them, using a low voltage, high current, and therefore a positive grid voltage, I was able to measure that the tubes exhibited "normal" curves like those of Eimac (they are metallic Eimacs). So, apparently, the tubes are not dead. ? Here's the principle of the bias system I use.
? I tested it with a single tube (it's easy) and I'll do it again. What I noticed then was that the gain was lower (why?):
? For only one tube, CW (1900 V) ? 9 W -> 100 W? Ia=170 mA (10.4 dB) 23 W -> 200 W? Ia=220 mA Ig=10 mA 39 W -> 250 W?? Ia=230 mA ? For only one tube, SSB (2600 V) ? 8 W -> 100 W Ia=180 mA (10.9 dB) 18 W -> 300 W Ia=230 mA (2550V) 31 W -> 300 W Ia=270 mA (2500 V) ? That's why I went back to the two-tube situation. I don't have any 4-250Zs, and I wanted to stay on the ground grid.
|
Re: Drake L7 [2 x 3-500Z] power ?
Or run a pair of cheaper 4-250"s.
Hoping I don't get beat up for this question. If all you need or can have is 500 watts would it be better running one tube?
Your tubes are dead?
73, Alek VK6APK.
On 28/04/2025 8:48 pm, Fran?ois via
groups.io wrote:
Make sure
the input circuit is lined up with the proper output band.
?
On
the input side, it seems fine. I'm driving L7 with
an FTDX-3000. I performed a TUNE, forcing the RLY relay to
close, and I have a VSWR of 1.
?
Test
conditions:
¡¤????????
Idle:
2600 V, 140 mA for a 6.5 V bias.
¡¤????????
At
the output, I'm on a 50-ohm dummy load; the L7 doesn't
indicate any output VSWR.
?
However,
I just noticed that on the 7.100 MHz band where I was
testing, the LOAD capacitors (C4, C47) are at their maximum.
I checked; they are indeed in parallel on this 40 m band.
The amplifier can't output more than 400 W.
?
On
3.650 MHz, the same problem: this LOAD capacitor is at its
maximum. The amplifier peaks at 400 W for 400 mA at 2300 V
and 25 W input.
?
At
14,200 MHz, the LOAD capacitor is at its midpoint, and a 25
W input produces 500 W (2300 V, 390 mA).
?
I
don't know what to think anymore.
De
la part de
mike repinski via groups.io
·¡²Ô±¹´Ç²â¨¦?: lundi 28 avril 2025 13:37
|
Re: Drake L7 [2 x 3-500Z] power ?
Hoping I don't get beat up for this question. If all you need or can have is 500 watts would it be better running one tube?
Your tubes are dead?
73, Alek VK6APK.
On 28/04/2025 8:48 pm, Fran?ois via
groups.io wrote:
Make sure
the input circuit is lined up with the proper output band.
?
On
the input side, it seems fine. I'm driving L7 with
an FTDX-3000. I performed a TUNE, forcing the RLY relay to
close, and I have a VSWR of 1.
?
Test
conditions:
¡¤????????
Idle:
2600 V, 140 mA for a 6.5 V bias.
¡¤????????
At
the output, I'm on a 50-ohm dummy load; the L7 doesn't
indicate any output VSWR.
?
However,
I just noticed that on the 7.100 MHz band where I was
testing, the LOAD capacitors (C4, C47) are at their maximum.
I checked; they are indeed in parallel on this 40 m band.
The amplifier can't output more than 400 W.
?
On
3.650 MHz, the same problem: this LOAD capacitor is at its
maximum. The amplifier peaks at 400 W for 400 mA at 2300 V
and 25 W input.
?
At
14,200 MHz, the LOAD capacitor is at its midpoint, and a 25
W input produces 500 W (2300 V, 390 mA).
?
I
don't know what to think anymore.
De
la part de
mike repinski via groups.io
·¡²Ô±¹´Ç²â¨¦?: lundi 28 avril 2025 13:37
|
Re: Drake L7 [2 x 3-500Z] power ?
Your tubes are dead?
73, Alek VK6APK.
On 28/04/2025 8:48 pm, Fran?ois via
groups.io wrote:
toggle quoted message
Show quoted text
Make sure
the input circuit is lined up with the proper output band.
?
On
the input side, it seems fine. I'm driving L7 with
an FTDX-3000. I performed a TUNE, forcing the RLY relay to
close, and I have a VSWR of 1.
?
Test
conditions:
¡¤????????
Idle:
2600 V, 140 mA for a 6.5 V bias.
¡¤????????
At
the output, I'm on a 50-ohm dummy load; the L7 doesn't
indicate any output VSWR.
?
However,
I just noticed that on the 7.100 MHz band where I was
testing, the LOAD capacitors (C4, C47) are at their maximum.
I checked; they are indeed in parallel on this 40 m band.
The amplifier can't output more than 400 W.
?
On
3.650 MHz, the same problem: this LOAD capacitor is at its
maximum. The amplifier peaks at 400 W for 400 mA at 2300 V
and 25 W input.
?
At
14,200 MHz, the LOAD capacitor is at its midpoint, and a 25
W input produces 500 W (2300 V, 390 mA).
?
I
don't know what to think anymore.
De
la part de
mike repinski via groups.io
·¡²Ô±¹´Ç²â¨¦?: lundi 28 avril 2025 13:37
|
Re: Drake L7 [2 x 3-500Z] power ?
An increase in anode
current increases the negative feedback action of a grounded grid amplifier.
Gain is also effected by
the efficiency of the input and output circuits,
?
73
Peter, DJ7WW
?
?
Indeed,
by increasing the input power, it outputs more.
?
¡¤???????
21.200 MHz 40W -> 700 W 470 mA 12.4 dB 2250 V
¡¤???????
7.100 MHz 40W -> 650 W 450 mA 12.1 dB 2250 V
?
We
are no longer in a linear range since up to 400 W, the gain is 13 dB.
?
Fortunately,
your advice helped me; I thank you for it because I'm regaining confidence. My
final (operational) objective is 500 W: the power authorized in France.
?
PS:
There is no ALC connected.
|
HaL Mandel