Re: Building my first amplifier. Where to start?
On 12/23/2023 7:09 AM, Floyd - K8AC wrote: The older ARRL handbooks are a good source of amplifier circuits and info.? I have a 2004 Handbook with some interesting amplifier circuits. I would interject that The Radio Handbook, edited by Bill Orr and/or "Editors & Engineers", is generally much more informative than almost any of the ARRL handbooks for amplifier circuitry, in particular. Various editions are available from time to time on epay at modest prices. The RSGB handbooks can also yield some valuable insight but are generally geared toward legal-limit power levels. Seems to me that just a single GU5B will deliver the legal limit easily. Agreed... they seem rated at 3 kW per tube...?? And all of the specs I've seen indicate the tube should be installed with anode down. I would venture to say that your MOST VALUABLE "insight" would probably be to make friends with a ham/amplifier builder within driving distance who knows what they are about. Yes, easier said than done, especially these days with the older, more-experienced folks dying out left and right... On your side of the pond, for high power schtuff, G8WRB comes to mind, but I haven't heard of nor seen anything from him for years. G3SEK is another but I believe he's mostly-retired from homebrewing..?? Try doing a Yahoo search using the various high power Russian transmitting tube numbers and many other European builders will come up... some of whom are even still around!! 73, Steve K0XP
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Re: Building my first amplifier. Where to start?
I'm sure you'll get a lot of input from real experts today, but I will give you a few high level comments.? Check out w8ji.com and read everything there about amplifiers.? Tom designed many tube amps for Ameritron and others over the years and is a good source of practical knowledge.? Also, read everything you can find by VE7RF.? He has written a lot on eHam amplifiers forum and elsewhere on building large amplifiers.? The older ARRL handbooks are a good source of amplifier circuits and info.? I have a 2004 Handbook with some interesting amplifier circuits.? On Facebook, look for the group "Amplifier Building and Homebrewing" - lots of good info there and you can converse with W8JI on difficult amplifier questions.??
Seems to me that just a single GU5B will deliver the legal limit easily.? I see that someone in Europe is selling sockets for that tube although they are quite expensive.? One area of concern is always the plate choke and it's a challenge to obtain one or build one that works properly on all the bands without resonances that can destroy them.? W8JI has good info on that.? You probably know that you won't be able to obtain tune and load capacitors at the needed voltage level and the capacitance range shown in your diagram.? Typically fixed capacitors are switched in for the lower band or two.? A good example of a fairly modern tube amp with these considerations covered can be found at AlphaRFSystems.com.? Here's a link to the Alpha 99 schematic:?.? That's a tetrode amp, but the site includes others info on their earlier triode amps such as the Alpha 86 and Alpha 89.??
To the questions "Am I mad?".? Maybe not, but you will be by the time the project is finished!
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Building my first amplifier. Where to start?
Hi guys, I have been subscribed to this list and reading messages for some time, but I believe this is my first message, so hello all. I am a ham based in the UK and have been interested in amplifiers for some time. I have a somewhat basic understanding of their operation if I'm honest, and currently own a linear amps UK 811 hunter. It uses 4 off 811 tubes, and runs very well. I understand 811's are somewhat delicate, and so I tread lightly with them.
I have always had a notion of building my own hf multiband amplifier covering 80 to 10 ideally.? I have been gathering parts that might someday be useful such as hv transformers, power supply hv capacitors, door knob caps of various values and some big vacuum caps etc. I don't have everything, but I guess I'm on the way. This approach makes things seem less expensive :) .
When it comes to tubes, I have also managed to collect some "interesting" items. I have a 3cw 30,000 and some gu5b's. The 3cw30,000 is clearly way too big (is there such a thing :) ) but the gu5b's might be about right.?
With the power supplies I have I can supply options. 2.8kv DC, 4.7kv DC, 5.5kv DC. All from a 20kva rated transformer, and voltages quoted are bridge rectified at zero load, not voltage doubled, so I have plenty of supply capacity.? I could tweak things to get intermediate voltages if useful. I am yet to collect filament supplies, and the thought of a 6.3v or similar high amp supply puts me off so I guess that rules out the 3cw30,000 or similar.
I have been told to start with a triode amplifier as a tetrode is a much more complex beast, which with it's screen supplies etc I can understand.? I have good metal working tools and equipment (Bridgeport mill and welding kit etc) and some electrical test kit including HV probes and a nano van and an old scope.?
Anyhow, I'm keen to learn as much as I can before I start off on this adventure, can you recommend any good books that are practical in their approach to hf amplifiers? I don't mind maths, I'm an engineer , but practical examples helps set context in my mind.
I have seen this diagram (attached) to an amplifier based on 2 off gu5b tubes. Obviously input circuits aren't described, but I guess it's a start?
Goal is something that will easily do the new 1kw UK limit. 2kw might be a nice max power rating. Am I mad??
Seasonal greetings all, des.?
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On Thursday, December 21, 2023, 10:14 PM, NI5L <ni5l@...> wrote: Gentlemen,
I want to thank you all for your input and help and especially to Lou for giving me some critical information. I gave the amp a road test today with a friend on 6 meters and he said it sounds clean. I drove it for 500 watts out and it ran great. I am going to leave it there and hope that 6 meters will be better next season out here in the desert.
73 all and Merry Christmas
Warren / NI5L
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Gentlemen,
I want to thank you all for your input and help and especially to Lou for giving me some critical information. I gave the amp a road test today with a friend on 6 meters and he said it sounds clean. I drove it for 500 watts out and it ran great. I am going to leave it there and hope that 6 meters will be better next season out here in the desert.
73 all and Merry Christmas
Warren / NI5L
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On 12/21/2023 5:31 AM, Louis Parascondola via groups.io wrote: NO NO NO. Not grid driven. ?Cathode driven! Neither?Carl or myself did grid driven! ?It was cathode driven. ?Yes I know 20?watts drive sounds crazy but handling the bit of positive feedback with the gain at proper loading kept it stable. ?He said to find the right spot and leave it alone else you might find yourself in trouble. ?It could have been even better with solidly grounded grids rather than floated but hey. OK, thanks for clarifying that, Lou, as it wasn't clear before. 73, Steve K0XP
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NO NO NO. Not grid driven. ?Cathode driven! Neither?Carl or myself did grid driven! ?It was cathode driven. ?Yes I know 20?watts drive sounds crazy but handling the bit of positive feedback with the gain at proper loading kept it stable. ?He said to find the right spot and leave it alone else you might find yourself in trouble. ?It could have been even better with solidly grounded grids rather than floated but hey.
On Wednesday, December 20, 2023, 11:11 PM, Steve <k0xp@...> wrote: On 12/20/2023 6:18 PM, Louis Parascondola via groups.io wrote:
> ........... There¡¯s quite a bit of regeneration but the skill
> in?building them was to keep them from taking off when loaded for
> maximum output. ?Carl kept his recipe for getting SB200¡¯s to work on
> ?6 meters as much of a sectet as Mrs. Paul¡¯s cheesecake.
Yup; he was never real open about how he did some of the "successful"
schtuff he was able to accomplish.
> I¡¯ve probably converted?half as many as Carl did and 18-20 watts gave
> you?about as much output as you¡¯d dare.
So, Lou: are you saying that you believe Carl converted this "SB-206" to
full grid-driven instead of grounded grid?? If so, that certainly does
help explain why tuning seems so touchy; I wouldn't have believed that
if you hadn't mentioned it.
Tell us, Lou... did you modify yours to grid-driven, or were yours
grounded grid??
73,
Steve K0XP
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On 12/20/2023 6:18 PM, Louis Parascondola via groups.io wrote: ........... There¡¯s quite a bit of regeneration but the skill in?building them was to keep them from taking off when loaded for maximum output. ?Carl kept his recipe for getting SB200¡¯s to work on ?6 meters as much of a sectet as Mrs. Paul¡¯s cheesecake. Yup; he was never real open about how he did some of the "successful" schtuff he was able to accomplish. I¡¯ve probably converted?half as many as Carl did and 18-20 watts gave you?about as much output as you¡¯d dare. So, Lou: are you saying that you believe Carl converted this "SB-206" to full grid-driven instead of grounded grid?? If so, that certainly does help explain why tuning seems so touchy; I wouldn't have believed that if you hadn't mentioned it. Tell us, Lou... did you modify yours to grid-driven, or were yours grounded grid?? 73, Steve K0XP
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Yup! Leave well enough alone.
On Wednesday, December 20, 2023, 10:47 PM, NI5L <ni5l@...> wrote: Yeah...I suffer from mess-with-it-itis sometimes but not in this case.? :)
If it ain't broke, don't fix it.
Warren
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Yeah...I suffer from mess-with-it-itis sometimes but not in this case.? :)
If it ain't broke, don't fix it.
Warren
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There should be about 70-90 ma. ?of idle current. I¡¯d leave it alone.
On Wednesday, December 20, 2023, 9:39 PM, NI5L <ni5l@...> wrote: Thanks for that, Lou. And I re-read the meter explanation in the Heathkit manual and saw what you said. The end of the white range is 100 mA.
?This may or may not be an issue but I do not show any idling plate current. Is that a problem? If it is, is there an adjustment like on the SB series radios?
I will tune it up like you said and be happy with it. I have a friend about 130 miles from me with a nice 6 meter array ad I am going to see if the audio is clean. If it is, I'll just leave it alone.? :)
Thanks, guys.
73
Warren / NI5L
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Thanks for that, Lou. And I re-read the meter explanation in the Heathkit manual and saw what you said. The end of the white range is 100 mA.
?This may or may not be an issue but I do not show any idling plate current. Is that a problem? If it is, is there an adjustment like on the SB series radios?
I will tune it up like you said and be happy with it. I have a friend about 130 miles from me with a nice 6 meter array ad I am going to see if the audio is clean. If it is, I'll just leave it alone.? :)
Thanks, guys.
73
Warren / NI5L
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Skip, he is reading the grid current wrong!!!!!! ?THE SB200 amp does not have a graduated scale for grid current!!!!!! It only has a white area as a safe zone. ?The last mm of the white zone is 100 ma. ?But it¡¯s NOT on the scale.
On Wednesday, December 20, 2023, 7:03 PM, Steve <k0xp@...> wrote:
Something doesn't sound right... you shouldn't be able to get 500
mils grid current and still have working tubes, ESPECIALLY with
only 18 watts drive... That's a RIDICULOUSLY-LOW amount of drive;
most of us are proud to get 650 mA plate current from a pair of
new 572Bs with 65 watts drive power on the HF bands! For the most
part, follow the Heath SB200 manual tuning instructions; except
that you will undoubtedly find you get much more output power by
peaking the plate tuning rather than dipping the plate.
Try increasing the loading capacitance to reduce the grid current
below half-scale, as you peak output with the plate tuning. SLOWLY
increase drive, keeping grid current at or below half-scale,
increasing loading slightly again (grid current should decrease
slightly as you increase loading capacitance), then peaking output
power with the plate tuning.
My guess is you aren't reading the grid meter right; I can't
believe Carl would have messed up the grid current meter scale
that badly. Let's put it this way for now... keep the grid current
reading below about half scale on the grid meter, whatever that
may be.
You can increase drive until the output does not also increase
but by then, you may be running the tubes real hard. I'd keep them
down to no more than 700 watts output under "rare DX pileup"
conditions, and more like 600 watts when working common schtuff
like North Carolina or Arkansas. For Nieu Yawk/Nieu Joisey/Pennsy,
I'd turn the amp off? 8-D
73,
Steve K0XP
On 12/20/2023 3:30 PM, NI5L wrote:
OK. Thanks for the replies, guys. I am getting 600 watts out at 18
watts of drive with the load backed off CCW ~25 watts from peak
(per the instructions). The grid current is at 500 mA. The plate
current is 650 mA.
Are these acceptable numbers to help the tubes live longer???
Thanks for any input.
Warren / NI5L
--
See my QRZ.com page at
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Warren, at 50 mhz the neutralization on 572b tubes?is way out in outer space. ?It¡¯s bad enough on 10 meters let alone on 50mhz. ?That said, you can¡¯t expect a dip in the plate at maximum output¡¯. So the proper way to load it is to peak the load and tune for maximum output then try to reduce the grid current a bit and repeak the plate fo maximum output. ?You came much too late to late to this party. ?Both myself and Carl converted many of those SB200¡¯s to 6 meters. ?The trick is to?make it stable at the maximum output point and as Carl said, LEAVE?IT ALONE. ?As long as the plates keep?from getting cherry red you¡¯ll be fine. ?There¡¯s quite a bit of regeneration but the skill in?building them was to keep them from taking off when loaded for maximum output. ?Carl kept his recipe for getting SB200¡¯s to work on ?6 meters as much of a sectet as Mrs. Paul¡¯s cheesecake. ?I¡¯ve probably converted?half as many as Carl did and 18-20 watts gave you?about as much output as you¡¯d dare. ?Keep the output peaked and the plates dark and you¡¯ll be fine. ?This is just another mystery of faith. ?Lou
On Wednesday, December 20, 2023, 7:55 PM, Chuck Neal <cdoneal@...> wrote: This is interesting¡was this amp modified for grid drive instead of grounded grid?? ? Another possibility is that there could be a bit of positive feedback, not enough to cause self oscillation but enough to generate more gain. ? Agreed, 18W for 600 W out isn¡¯t possible for a normal functioning grounded grid amp with 572B¡¯s.? Their gain at best in GG is perhaps 12 dB. which would yield maybe 270 watts with 18W drive.? An unintentional positive feedback of 3+ dB would do it though¡.and the tuning would be VERY sensitive. ? -Chuck ? From: [email protected] [mailto:[email protected]] On Behalf Of NI5L
Sent: Wednesday, December 20, 2023 7:40 PM
To: [email protected]
Subject: Re: [ham-amplifiers] SB-206 ? Steve,
With no REL PWR function, I have just been peaking everything up using a watt meter. Like you, I am a little bit curious as to why it only takes 18 watts of drive to get 600 out. I just wrote it off to this being a 6-meter VHF amp.? It has a VERY narrow bandwidth... 50.000 to 50.500 according to the plate on the amp's face., which is perfect for me. I have tried peaking the grid and dipping the plate but I come up with some pretty hairy plate current when I do that. I'm just really nervous about killing the tubes or the tank circuit. After reading what Lou said, now I am even more puzzled as to what references to use when tuning this thing. Carl said that once it is tuned, leave it alone and that the frequency range would be covered if tuned at 50,200 or so. I will try what you said next time i get the amp online. Currently it is going to be an off-desk amp when I need power on 6 meters since we have very few 6 mete DX openings like the east coast does. Spotlight openings are few and far between out here in southeast Arizona.
Thanks and 73
Warren / NI5L
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Chuck,
The grid question is a good one and there is NO schematic of the conversion. It is written on the "manual" page in big script that there is no schematic. That is part of the reason I am puzzled about this amp. The "manual" claims between 10 and 12 dB gain in this configuration. As everyone probably figured out, I am not much of a technician and am trying to figure out what is going on with this unusual amplifier so that I don't kill it. I could pull it out of the cabinet and see if the grids are still grounded. I may do that just to try and get some more info to work with.
73
Warren / NI5L
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This is interesting¡was this amp modified for grid drive instead of grounded grid?? ? Another possibility is that there could be a bit of positive feedback, not enough to cause self oscillation but enough to generate more gain. ? Agreed, 18W for 600 W out isn¡¯t possible for a normal functioning grounded grid amp with 572B¡¯s.? Their gain at best in GG is perhaps 12 dB. which would yield maybe 270 watts with 18W drive.? An unintentional positive feedback of 3+ dB would do it though¡.and the tuning would be VERY sensitive. ? -Chuck ?
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From: [email protected] [mailto:[email protected]] On Behalf Of NI5L
Sent: Wednesday, December 20, 2023 7:40 PM
To: [email protected]
Subject: Re: [ham-amplifiers] SB-206 ? Steve,
With no REL PWR function, I have just been peaking everything up using a watt meter. Like you, I am a little bit curious as to why it only takes 18 watts of drive to get 600 out. I just wrote it off to this being a 6-meter VHF amp.? It has a VERY narrow bandwidth... 50.000 to 50.500 according to the plate on the amp's face., which is perfect for me. I have tried peaking the grid and dipping the plate but I come up with some pretty hairy plate current when I do that. I'm just really nervous about killing the tubes or the tank circuit. After reading what Lou said, now I am even more puzzled as to what references to use when tuning this thing. Carl said that once it is tuned, leave it alone and that the frequency range would be covered if tuned at 50,200 or so. I will try what you said next time i get the amp online. Currently it is going to be an off-desk amp when I need power on 6 meters since we have very few 6 mete DX openings like the east coast does. Spotlight openings are few and far between out here in southeast Arizona.
Thanks and 73
Warren / NI5L
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Steve,
With no REL PWR function, I have just been peaking everything up using a watt meter. Like you, I am a little bit curious as to why it only takes 18 watts of drive to get 600 out. I just wrote it off to this being a 6-meter VHF amp.? It has a VERY narrow bandwidth... 50.000 to 50.500 according to the plate on the amp's face., which is perfect for me. I have tried peaking the grid and dipping the plate but I come up with some pretty hairy plate current when I do that. I'm just really nervous about killing the tubes or the tank circuit. After reading what Lou said, now I am even more puzzled as to what references to use when tuning this thing. Carl said that once it is tuned, leave it alone and that the frequency range would be covered if tuned at 50,200 or so. I will try what you said next time i get the amp online. Currently it is going to be an off-desk amp when I need power on 6 meters since we have very few 6 mete DX openings like the east coast does. Spotlight openings are few and far between out here in southeast Arizona.
Thanks and 73
Warren / NI5L
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Lou,
I am tuning it to keep the grid current at 500 mA or less. The white area tops at 500 mA so that is what I have been referencing. This is a very touchy tank circuit! The amp came with some pencil marks (!) for reference when tuning so I used them. The final tune points are not off from those marks by much at all. I don't plan on running anything over 600 watts to help preserve the tubes as much as possible. I guess the only meter function that is relevant is the HV.? :)
Thanks for the insight.
Warren / NI5L
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Something doesn't sound right... you shouldn't be able to get 500
mils grid current and still have working tubes, ESPECIALLY with
only 18 watts drive... That's a RIDICULOUSLY-LOW amount of drive;
most of us are proud to get 650 mA plate current from a pair of
new 572Bs with 65 watts drive power on the HF bands! For the most
part, follow the Heath SB200 manual tuning instructions; except
that you will undoubtedly find you get much more output power by
peaking the plate tuning rather than dipping the plate.
Try increasing the loading capacitance to reduce the grid current
below half-scale, as you peak output with the plate tuning. SLOWLY
increase drive, keeping grid current at or below half-scale,
increasing loading slightly again (grid current should decrease
slightly as you increase loading capacitance), then peaking output
power with the plate tuning.
My guess is you aren't reading the grid meter right; I can't
believe Carl would have messed up the grid current meter scale
that badly. Let's put it this way for now... keep the grid current
reading below about half scale on the grid meter, whatever that
may be.
You can increase drive until the output does not also increase
but by then, you may be running the tubes real hard. I'd keep them
down to no more than 700 watts output under "rare DX pileup"
conditions, and more like 600 watts when working common schtuff
like North Carolina or Arkansas. For Nieu Yawk/Nieu Joisey/Pennsy,
I'd turn the amp off? 8-D
73,
Steve K0XP
On 12/20/2023 3:30 PM, NI5L wrote:
OK. Thanks for the replies, guys. I am getting 600 watts out at 18
watts of drive with the load backed off CCW ~25 watts from peak
(per the instructions). The grid current is at 500 mA. The plate
current is 650 mA.
Are these acceptable numbers to help the tubes live longer???
Thanks for any input.
Warren / NI5L
--
See my QRZ.com page at
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The grid current?isn¡¯t 500, it¡¯s has?nothing to do with the scale reading. ?As long as it¡¯s in the white area it¡¯s ok. ?With the 572b tube it¡¯s the temperature of the plates that is the driving factor, not so much grid or plate current. ?The572b has a very robust grid and plate structure. ?As long as the plates don¡¯t glow bright red and stay relatively dark,you are fine. 700 watts on 6 meters is about the safe level but not for digital modes!! ?SSB 800 pep is fine.
On Wednesday, December 20, 2023, 6:30 PM, NI5L <ni5l@...> wrote: OK. Thanks for the replies, guys. I am getting 600 watts out at 18 watts of drive with the load backed off CCW ~25 watts from peak (per the instructions). The grid current is at 500 mA. The plate current is 650 mA.
Are these acceptable numbers to help the tubes live longer???
Thanks for any input.
Warren / NI5L
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Floyd - K8AC
