Great video. I'd be interested if you would be selling the unpopulated protection board. I'm restoring 2 PL400's, and really like your design. Thanks Richard
Dear Sir, I would like to ask a question about your protection circuit. What is the electrical current specification for the 1.75uH inductor? Or if you made it yourself, what is the AWG, number of turns, and diameter? I would be very grateful if you allow me to use your design to add to my amplifier. Thank you very much.
I noticed the idea of "water tight" repeated. Ive learn designing to minimize water infiltration BUT include a path for water to exit helpful. An example, ive installed "water tight" power outlet boxes only to find water finds a way in, but no way out and corrodes the internals.
As I used my cheap Harbor Freight Flag pole, for an antenna mast, I drill and used pins to go thru the mast, instead of fighting with Hose clamps ! No more worry of variable wind speeds vibrating mast to collapse ! Just a thought ! As everyone has their own way of doing things ! The pins I used, have metal rings on one end, making for easy disassembly ! 👍😉
Thanks, The readout in one of my 7950's has totally died. The radio becomes worthless without a way to create a remote readout. Kenwood used carbon based ribbon cables to the readout back in the day. Totally a bad idea.
Hello RCD66, I like your commentary as it is simple but very much understand-able! I have a question regarding W8Ji's neutralizing. W8JI called out 15T #28 wire however, your schematic calls for twisted pair 30T bifilar wound? Can you help me understand the process bifilar wound, to me, it imply 2 wires side-by-side wound Vs. twisting a pair of 30T of 28 gauge wire looping around the toroid's loop core. Also looping a bifilar wound15T Vs. 30T of 28 gauge wire is a substantial change, perhaps 30T was required? Thank You for your time! :) 73's AH6BS (blue-sky *LOL*)
Change the tubes, I bet it works fine on ten. Use stock parasitic chokes. The input coils are tuneable you don't need a tuner, check your input coax length. Yes you need a keying interface. Learn more before you post nonsense. Look at those bullshit parasitic chokes. Make stock ones !
I like that you are using compactrons, we need to continue to utilize the remaining NOS tubes to do our bidding. I experiment myself but usually on guitar amps.
Craig, I remember repairing Marantz receivers where the speaker protection relay would arch when the and burn up. It was caused by a diode in the bias circuit that was intermittent and caused the dc to slam to the minus or plus rail. When the relay opened, it provided a short to the speaker and a good path to ground for the arch.
What was your method to adjust the input circuit? I have an SB 200 and it runs great on 80, 40, and 20 but 15 and 10 not so well. So what is the process to trouble shoot? KN6YKE
You need a pure 50 ohm source of a minimum of 10W and adjust the input components for a minimum SWR on the input to the amp for each band. At the same time you must peak the output of the amp for maximum into a pure 50 ohm dummy load as the output tuning of the amp reflects changes to the input. It becomes a balancing act between the output and input until you get it right.
My 80-10m efhw shows an swr less than 2 at 80m and 1.5 or less on the harmonics. and starts at 10ft up to 25ft in height. I use a homemade 56:1 unun. I have a choke on a 3ft jumper under the 56:1 unun and a 33ft counterpoise wire which am going to change to a 66ft 1/4 wave at 80m and bring down the swr even more on 80m. And not rely on the coax for the counterpoise being it is only 50ft long. I also run a choke at the shack end of the coax. I am also going to shorten the132ft element to bring several bands into the center of the bands and adjust the upper band tuning coil to keep the upper bands down in their respective bands. I could just eliminate all the extra stuff by cutting the main element in half and put a 300 to 500 pf high voltage cap in the middle and call it a day.
Yes they did, and they are a bit more popular and command more money . I have a 700b myself that I am doing all the white oak and a few other upgrades .
Fantastic! I admire your approach of attempting to maintain the original design with tasteful enhancements. When and where can we buy the pcb’s you built and incorporated!?!?!? Thanks again for sharing 👍
I bought a used one sometime ago that was dead, I changed out the fuses because they were blown but I have not even powered it up lol.... I guess haven't really been curious about whether it works or not until now.
If the speaker fuses were blown.. don't bother testing it. You've got something shorted somewhere. I find most often it's a pre-driver failure. It won't always cook the output devices, BUT I recommend you check every transistor on the main board, and all of the outputs. The first TO-3 output transistors (RCA 410's) are drivers for the main outputs. Those usually don't go bad. If it's just the main fuse that went bad, it may have been inrush current trying to reform the old filter caps. Bring it up slowly on a variac or use a dim bulb to limit current. You'll likely need new filter caps. Easy to do and easily available.
Thank you for all your work testing and selecting the values to make the amp work well with newer radios. I just finished restoring a SB-200 that had been in storage for about 18 years. It works well but as you have shown the input circuits leave a lot to be desired. I have tried tuning the input slugs but they are all firmly stuck in position. Did you have to work to release you slugs? What method did you use to loosen them? I also went through your first video several times to gleam information that helped me with my amplifier. 73 Ken WA1BFS
You should have a pot on the output of the “dirty” stage so the amount of gain fed to next stage is adjustable. Most guitar players would like to control that.
Very interesting video, I'm searching something like this from months. Is there the possibility to have the final schematic of this project? It would be a fantastic thing for an electronic lover. Thank you
If the power lines were not between my back lot and the lake lot, a EFLW would be great. I have a bid on the lot next door which, If I get it, would solve lots of issues. Thanks
You could pick up submarines with that. I Haven't a clue what the impedance would be. Stray high voltage would be of a concern. If you remember, Art Bell made an antenna like that, lots of induced high voltage. Good luck. @@kevinaponte7078
Can you make your PDF available that shows the mark-ups for the modifications? That would be very helpful. If not, could you show full screen views on your next post of each of the mods? Thanks in advance. Steve, WA0A
Looking forward to that post about the input circuit matching CIRCUITDESIGNER! I am in the process of buying an SB-201 from a buddy and I also have a IC-745 I will be driving the amp with. Steve, WA0A
I like your Thermistor in the filament circuit. I've added a small 12V, 1A DC supply, replaced the T/R relay with one having a 12V coil and a small solid state relay to drive that relay. The internal 12V is used as pullup on the SSR internal LED so the modern radio only sources 7.5mA with its' open collector transistor. I kept the RF grid grounding with SM caps but DC grounded them with chokes. For DC bias applied +50 DC during standby, or a 10W, 10V Zener diode bias through a 3rd T/R relay to the filament transformer's center tap. This make the Q current much lower (about 40mA) so the tubes don't glow as much and stay much cooler. The RF output doesn't contain out of band emission.
Nice project and video, thanks! Love the triple triode. I think the opamp might not be needed. The output stage, a cathode follower, has a low (<1K ohm I'd guess) output impedance. And the voltage feedback network makes that impedance even lower. The output impedance of the tube part can be measured by applying a 10K or 2K load and measuring the voltage change before and after the output resistor. Cheers!
I did jump out the op amp for some testing and found the RIAA curve shifted somewhat when I applied a 10K load so I stayed with the op amp as an impedance buffer. Thanks
Yea, This supply had common grounds so isolation wasn't necessary plus its powered from a 12v wallwort. Many of my other switchers such as the one in the tube amplifier design has what you described.
The transformer is designed to limit start up current, you don’t need a step start. The best thing I ever did to an sb200 was to directly ground the grids! Using a stock set of Cetron tubes and tweaking the inputs a bit the amp was perfectly stable. Power output shot up drastically. I loaded the amp up for performance purposes to maximum grid current without going out of the white zone. Power out figures were 80m-950watts pep 40m-900pep 20-900 pep15m-850watts pep and 10m -750-800pep. If you throttled the drive back to be conservative 750-850pep output on all bands it will just load along.
Sounds like something to try for more power. My only concern would be the 2nd and 3rd harmonics. I have a Rigol DSA815 Spectrum Analyzer that could check that. My big concern was getting a 1:1 match of 50 ohms between the radio and the amplifier on all bands. I finally accomplished that and will post soon.
I have thw same identical model . Powers on, but i have not used an antenna. I want to have this restored. I am not mechanically inclined. Can you recommend a place to send it? Thanks.
Was this project a success? Approx 1 year ago Blackstar Amplification released the St. James, guitar tube amp describing it as lightweight with no noise or hum. Blackstar swapped the transformers for SMPS. Do you offer these types of modification services? I recently acquired a Marshall JVM 215c. Love the sound but hate the weight and noise.
That sounds like a good business. Getting the 5 to 600v plate voltage is challenging for the transformer design but SMPS for tube amps is very practical . If I was 20 years younger and not retired I would kick out a few designs. Thanks
Nice job. Congratulations on your new antenna. With a little fine tuning and an antenna tuner, it looks like you’ll have stealthy setup covering 3-4 bands. I’m wondering about your electrical grounding though. The way I understand it you should have all your electrical grounds bonded to the main grounding point (usually at your mains panel EGC). Otherwise you have a ground loop condition which opens you up to the potential of a varying ground reference and RFI, not to mention ground voltage gradients and last but not least, code violations. You might want to look into it.
