Re: Drake L7 [2 x 3-500Z] power ?
You increase the output
power by increasing the drive power.
The anode pi circuit is
designed for about 1200W output at 2.5kV plate voltage.
That output is typical
for L4B and L7 amplifiers.
?
73
Peter
?
?
Hello
?
I've
already presented the refurbishment of this L7 amplifier here. I implemented a
cathode bias and connected the grids directly to ground. I noticed that,
regardless of the bias, I can't output more than 400 W.
?
At
7.100 MHz
·???????
The gain is 13 dB.
·???????
The plate voltage under load is 2450 V.
·???????
The plate current is 310 mA.
?
?
·???????
How can I increase the output power?
·???????
What do you notice on an amplifier equipped with 2 3-500Z tubes
in parallel?
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They look like 6360s, 10 watt push/pull VHF PA tubes.? I can’t be certain, though. ? QQE0312 ? -- F1AMM Fran?ois De la part de Mahlon Haunschild - N4ZK via groups.io
贰苍惫辞测é?: lundi 28 avril 2025 18:25
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Oh, gosh!
?
Poor babies!
?
Hal Mandel W4HBM
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They look like 6360s, 10 watt push/pull VHF PA tubes.? I can’t be certain, though.
Best regards
Mahlon - N4ZK
?
These tubes were literally dug up last weekend at a former "VHF Telegraphy" commercial site in the UK.
?
Does anyone recognise what they are ?
?
Ideally I'd like to know what equipment they were used in, date is likely 1960 - 1980, all the printing is lost to the rain/soil.
?
Tim?
?
?
?
?
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?
These tubes were literally dug up last weekend at a former "VHF Telegraphy" commercial site in the UK.
?
Does anyone recognise what they are ?
?
Ideally I'd like to know what equipment they were used in, date is likely 1960 - 1980, all the printing is lost to the rain/soil.
?
Tim?
?
?
?
?
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Re: Drake L7 [2 x 3-500Z] power ?
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.
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Re: Drake L7 [2 x 3-500Z] power ?
25 watts is NOT enough drive to get the load control up of full capacitance. ?You need to drive the amp with much more power. ?Once you head around 50 watts the load control will begin to go higher off 1 on the dial. ?80 watts or more is typical drive for a pair of 3-500 tubes.
On Monday, April 28, 2025, 8:48 AM, Fran?ois via groups.io <18471@...> 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
贰苍惫辞测é?: lundi 28 avril 2025 13:37
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Re: Drake L7 [2 x 3-500Z] power ?
It seems like the output circuit is off? The higher you go up in mhz the better the efficiency gets. can you see what it looks like on 15?
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
贰苍惫辞测é?: lundi 28 avril 2025 13:37
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Re: Drake L7 [2 x 3-500Z] power ?
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
贰苍惫辞测é?: lundi 28 avril 2025 13:37
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Re: Drake L7 [2 x 3-500Z] power ?
Make sure the input circuit is lined up with the proper output band.
I’m working on a pair of L7 amps right now and will be testing them today. ? I would like you to publish the results of your investigations. I cannot get more than 400 W out even when over-exciting the input. De la part de Louis Parascondola via groups.io
贰苍惫辞测é?: lundi 28 avril 2025 12:06
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Re: Drake L7 [2 x 3-500Z] power ?
I’m working on a pair of L7 amps right now and will be testing them today. ? I would like you to publish the results of your investigations. I cannot get more than 400 W out even when over-exciting the input. De la part de Louis Parascondola via groups.io
贰苍惫辞测é?: lundi 28 avril 2025 12:06
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Re: Drake L7 [2 x 3-500Z] power ?
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.
On Monday, April 28, 2025, 2:01 AM, Fran?ois via groups.io <18471@...> wrote: Hello ? I've already presented the refurbishment of this L7 amplifier here. I implemented a cathode bias and connected the grids directly to ground. I noticed that, regardless of the bias, I can't output more than 400 W. ? At 7.100 MHz ·???????? The gain is 13 dB. ·???????? The plate voltage under load is 2450 V. ·???????? The plate current is 310 mA. ? 
? ·???????? How can I increase the output power? ·???????? What do you notice on an amplifier equipped with 2 3-500Z tubes in parallel?
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Drake L7 [2 x 3-500Z] power ?
Hello ? I've already presented the refurbishment of this L7 amplifier here. I implemented a cathode bias and connected the grids directly to ground. I noticed that, regardless of the bias, I can't output more than 400 W. ? At 7.100 MHz ·???????? The gain is 13 dB. ·???????? The plate voltage under load is 2450 V. ·???????? The plate current is 310 mA. ? 
? ·???????? How can I increase the output power? ·???????? What do you notice on an amplifier equipped with 2 3-500Z tubes in parallel?
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Harbach Electronics And Homebrew HF Amps
Harbach Electronics has started their own FB group. "This is a place for people to post pictures of their Harbach kit installs, Homebrew ham pa projects and brainstorm ideas".
It's actually quite well done.? ?The kits need? a diagram, and some other minor tweaks in the documentation.
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Re: Commander HF-2500 meter lamps and HV PS
That’s a SB-1000. Just showing the dirt on the strip that I pulled off the relay.?
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Re: Commander HF-2500 meter lamps and HV PS
Hmmm alright. That doesn't look like a Commander HF-2500 with
3CX800A7s. ?
On 20/04/2025 6:10 am, KG2RG via
groups.io wrote:
toggle quoted message
Show quoted text
Hmmm, the relay is right there??
I do want to clean the relay. I cut strips of paper, saturate
them with DeoxIT, and clean the tint acts on the relays. They
are almost always dirty.?
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Re: Commander HF-2500 meter lamps and HV PS
Hmmm, the relay is right there??
I do want to clean the relay. I cut strips of paper, saturate them with DeoxIT, and clean the tint acts on the relays. They are almost always dirty.? 
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Re: Commander HF-2500 meter lamps and HV PS
No. Just remove the rear panel screws and fold the panel down to
get to the relay/s. There's also the relay on the control board.
Cheers, Alek.
On 19/04/2025 1:51 pm, KG2RG via
groups.io wrote:
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Show quoted text
Well, my goal was to just have the meters red in standby and
green when ?out of standby but the 1 set of the poles are bad on
the 2PDT standby switch.?
I don’t want colors changing between TX and RX but that could
potentially work but you would need to pull out the entire RF
deck to access the relay. The other issue is the limited current
on the 12V 1amp supply for the relay and meter lights.
?
Anyway, I may try to find a replacement switch that matches
the one in there now.
?Thank you for your info, it’s definitely possible.
on my SB-220, I have one of the meters go dark when in
standby. The standby on the SB-220 is a mod and it’s nice to
have the indication of the am in standby or not from the lights
in the meter. ?
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Re: Commander HF-2500 meter lamps and HV PS
Well, my goal was to just have the meters red in standby and green when ?out of standby but the 1 set of the poles are bad on the 2PDT standby switch.?
I don’t want colors changing between TX and RX but that could potentially work but you would need to pull out the entire RF deck to access the relay. The other issue is the limited current on the 12V 1amp supply for the relay and meter lights.
?
Anyway, I may try to find a replacement switch that matches the one in there now.
?Thank you for your info, it’s definitely possible.
on my SB-220, I have one of the meters go dark when in standby. The standby on the SB-220 is a mod and it’s nice to have the indication of the am in standby or not from the lights in the meter. ?
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Re: Commander HF-2500 meter lamps and HV PS
The solution is simple if you want the colours to change between
Tx and Rx. Install another small SPDT relay in parallel with the
keying relay and wire each strip through the contacts.
73, Alek VK6APK.
On 19/04/2025 9:03 am, KG2RG via
groups.io wrote:
toggle quoted message
Show quoted text
So I installed 2 LED strips that draw 66mA each. I tried to
utilize that standby DPDT but the one set of poles is shot.
Anyway, I’m just running both strips, red and green. I may drop
the voltage to the strips because they are so bright, but good
to be out of the dark on those meters.?
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HaL Mandel