Dedicated DIY Audio Thread

rocket sok
the model rocket show
eggtimer rocketry
the rocketry show
The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
jderimig said:
Yup, and illegal CB linears help dry up the supply of good ones. They were $1 each and the home-brew designs ran them at too high a plate current and burned up the supply, why not at a buck a tube, until they were all gone.
Click to expand...

I had a buddy who built high output alternators for car audio. He had a customer who put a motor in the back of his van with 7 alternators for his CB linears.
 
tsmith1315 said:
I had a buddy who built high output alternators for car audio. He had a customer who put a motor in the back of his van with 7 alternators for his CB linears.
Click to expand...
I wonder if the FCC ever cracked down on those guys? Someone missed a great opportunity selling HIGHEND CB microphone and antenna cables to them.
 
If this was a DIY kit I would love to own something of this great asthetic quality:
mKbUgaI.jpg
 
jderimig said:
I wonder if the FCC ever cracked down on those guys? Someone missed a great opportunity selling HIGHEND CB microphone and antenna cables to them.
Click to expand...

Pretty sure those guys were drug dealers who had more money than they knew what to do with. They'd have competitions, meet at a parking lot somewhere pull up next to each other and key their mic's at the same time. Like street racing, it was a thrill to get away with it. They couldn't stay long, or they'd get caught.
 
OMG,I learned so much in this thread I'll never use. I've spent stupid money chasing the audio dragon back in the day.
I've pinned The coax of a guy running a linear, even after I tore my gf's stereo receiver apart to install a filter. His wife would use it to order groceries from him at midnight. Kinda ruined the wine, cheese and firelight ambience. Hope it fried his unit. Damn, all those tubes...
Thanks for the education, I think.
 
As mentioned in a previous post the first amp I built used the 1625 tube which was the transmitter tube used in US WW2 aircraft. My father had 6 of those still in US Army Signal Corp packaging. Since then I have accumulated about 20 more off ebay at an average cost of about $4 each. My second amp will be a push-pull version using the same tubes.

The 3rd project will be more interesting and "balanced". The Germans in WW2 has some pretty sophisticated electronics also. Below is the transponder from a German IFF (Indentifcation Friend Foe) aircraft transponder. The transmitter tube (the one in the picture with the knob) was a very advanced Telefunken LS-50. It had a special plate that can dissipate 50W, a focused ray beam pentode and VERY rugged construction. A much better tube than the Allied 1625 for war duty. This tube as also used in German radar units that transmitted 300W pulses. At the end of the war the Soviets captured the Telefunken factory and moved all the factory equipment to the Soviet Union and produced this tube for another 45 years for the Soviet military and consumer electronics (Russian TV sweep tubes). After the fall of the eastern block European and later American audiophiles discovered the tube which was available in great quantities at very low prices ($1 per tube).


tScreenshot from 2023-05-02 19-02-18.png

Hard to buy stuff from Russia anymore but a large supply of these tubes are available from the Ukraine. So to help some Ukrainians I bought some from Ebay and they got out fine. This a pretty cool tube and they will be powering my speakers in the near future. Yes that is a knob on top to make it easy to grasp and replace. German engineering.

IMG_20230502_185318584.jpg
 
Here is a picture of the CED (Compound Electronic Device). Hybrid of a power beam tetrode or pentode, feedback resistors from plate to grid, and mosfet for signal drive to the cathode.

Results in almost perfect linear triode curves. Will post a final schematic and LTSpice simulation of THD. Its very low.

1684853300336.png
 
OverTheTop said:
Why not just use MOSFETs and cut out the middleman? Asking for a friend.
Click to expand...
Because the MOSFETs may not give him the characteristics he wants, just by themselves.

Tubes, or valves as our British friends call them, are not the distortion-laden, nasty-sounding devices that some people seem to think they are. Every component has its own idiosyncrasies and characteristics, including solid-state. An engineer designing a piece of equipment will take those characteristics into consideration and design around them. Designing only in solid-state limits what you can do with a design.
 
OverTheTop said:
Why not just use MOSFETs and cut out the middleman? Asking for a friend.
Click to expand...
In this topology the MOSFET is used as a voltage follower to drive the valve cathode instead of the traditional valve grid drive. There is no amplification done by the MOSFET. All the amplication duty is done by the valve.
 
Here is the hybrid circuit that I will likely build this fall into winter, right now my tube projects go on hiatus for the summer.

The front end takes a balanced input to a differential pair of pentodes (12GN7A) wired as triodes. They are biased by a solid-state current source which provides an almost perfect differential amp with very high CMRR. The output of the driver are fed to the gates of the output cathode MOSFET voltage followers. The output tubes are biased to be in class A push-pull to about 25W. There is NO stage negative feedback other than the local feedback in the output tubes from plate-to-grid.

The Spice simulation 1khz fundamental FFT plot (below the schematic) results in almost NO THD. The numerical calculation shows about 0.1% THD. Because of the class A bias there is also no crossover distortion possible.

1V rms input drives the amp to clipping so no pre-amp is needed. I will feed this amp directly from the balanced outputs of my DAC.

1684933895645.png
1684934425479.png
 
Last edited:
@jderimig suggested I might want to move this post over here instead of dedicated av.

I needed something to do so I bought an amp kit.

300B Class A from China via eBay. No instructions. Just the schematic.

Put the power supply together. It was popping the fuse when the tube went in so I ripped out the filter section today. Make it a little cleaner, maybe even fix the short when I put it back.
 

Attachments

  • IMG_1825.jpg
    IMG_1825.jpg
    141.6 KB · Views: 0
  • 71470792139__E67B5AF6-F207-432E-B7FB-672BA9E9001C.jpg
    71470792139__E67B5AF6-F207-432E-B7FB-672BA9E9001C.jpg
    247.7 KB · Views: 0
Alan R said:
@jderimig suggested I might want to move this post over here instead of dedicated av.

I needed something to do so I bought an amp kit.

300B Class A from China via eBay. No instructions. Just the schematic.

Put the power supply together. It was popping the fuse when the tube went in so I ripped out the filter section today. Make it a little cleaner, maybe even fix the short when I put it back.
Click to expand...
Why type and value is the coupling capacitor from driver to the 300B grid?
 
Alan R said:
Here's the schematic. My brother is a tube-head. He's the one that convinced me I could build this HAHAHA.. Anyway, he's helping with the debugging.

View attachment 601483
Click to expand...

Looking forward for your posts on this, keep us informed. What speakers are you going to use with this? You need one that will work well on the 5-8W you will get from this output.
 
jderimig said:
Looking forward for your posts on this, keep us informed. What speakers are you going to use with this? You need one that will work well on the 5-8W you will get from this output.
Click to expand...
Already planned for that. Picked up a pair of Klipsch R-15s. They are super sensitive 93db I think. They are temporarily employed as the front pair on the surround sound. I'm not in this for floor-shaking rock n roll.
 
Alan R said:
Already planned for that. Picked up a pair of Klipsch R-15s. They are super sensitive 93db I think. They are temporarily employed as the front pair on the surround sound. I'm not in this for floor-shaking rock n roll.
Click to expand...
That is great. Those speakers might have a challenging impedance load for the amplifier. Tube amps and speakers interact quite a bit. SET's with no negative feedback (like yours) prefer a flattish impedance load. They won't hurt your amp at all but the frequency response might be affected. The impedance in the midrange is quite high. This will load your output tubes less in this frequency range and shift their operating loadlines. It will likely still sound good but you may notice a difference compared to the solid state amp you are used to hearing them with. Your report will be interesting.

https://www.stereophile.com/content/klipsch-rb-15-loudspeaker-measurements
 
@Alan R Also just in case you do not know this, NEVER turn your tube amp on without a speaker or load connected to the speaker outputs. You can damage the output transformer or the output tubes.
 
Alan R said:
Ender 3. No resin, and I don't do ABS.
Click to expand...
Maybe a 0-11 graphic for a fixed bezel. That might be easier and you can use a quality knob then. I can cnc one with a v-carve bit. Or cut it into the back of clear acrylic so the top is pretty. If you give me a size and travel in degrees, I'll give it a go.
 
Last edited:
RocketScientistAustralia said:
Maybe a 0-11 graphic for a fixed bezel. That might be easier and you can use a quality knob then. I can cnc one with a v-carve bit. Or cut it into the back of clear acrylic so the top is pretty. If you give me a size and travel in degrees, I'll give it a go.
Click to expand...
I think thats what I was calling a backplate.
Cool. Thank you. I'll let you know when I get to that point.
 

Similar threads

Aksrockets
IT'S L2 TIME BABY!!!! - Shockwave 54 Build Thread - Introduction
2
Replies
39
Views
5K
Aksrockets
Aksrockets

Latest posts

Back
Top