The AM Forum

Hi guys,

do you like this layout?

(http://wavebourn.com/images/audio/gu50_amp_layout.gif)

http://wavebourn.com/images/audio/gu50_amp_layout.gif

I would move the small tubes back an inch or so. This will allow more room the wire them.

Thanks, interesting idea!

What if to move phase splitter tubes back one inch leaving indicators on the edge?

I would move the phase splitter tubes back between the input amp and output. This will allow more room to wire each socket.
I don't like stacking components around tube sockets. Too hard to work on. I like all the parts on one plane.

I will order PCBs for each channel of a phase splitter.

Here is the schemo:


(http://wavebourn.com/images/audio/gu50amp-phsp.gif)


http://wavebourn.com/images/audio/gu50amp-phsp.gif

Correction: 6N1P will be loaded on 27K resistors instead of 56K and powered from unregulated 375V, 6N6P will be used instead of 6N1P

Almost all stages are directly coupled for better stability on low frequency end.

Is this for hifi/guitar consumers?

If so, I'd leave the small tubes where they are, and mount them on a series of platforms made from L-brackets, arraged with the tallest in the middle (like an Olympic Gold Medal ceremony). I'd paint the chassis fire-engine red except for a bare strip of aluminum shaped like a "V".  Also I'd add a few jeweled pilot lights.

Thank you!

It is actually a vocal amp for concerts, 2X100W output. Also, I am going to target them as studio monitoring amps. Front panel will be made of Lexan. It will be fitted into a grilled 4U enclosure so all internals will be visible.

I'd be interested in hearing more about the studio monitoring aspects when it's complete.  She's gonna be a beaut!
Rick

Leave the tubes out near the edge so you have enough room for the tank circuit components

I can tell you now: unlike solid state amps it is immune to cellphones near speaker wires, it is the most significant advantage except warm tube sound.

Thank you!

I am going to order also perforated 4U enclosures for them, like Collins transmitters. The enclosure will be black, the chassis will be bright red.

Front panel made of lexan, with pair of volume knobs, power switch, and safety "ignition" key, like on this my breadboard:

(http://wavebourn.com/images/audio/gu50ampbg.gif)

http://wavebourn.com/images/audio/gu50ampbg.gif

Input and output sockets will be on rear panel

(2 for in, 2 for 4 Ohm, 2 for 8 Ohm, 2 for 16 Ohm) -- all TRS.

Tank circuits will be flat to fit inside of 1U chassis, here are breadboards:

(http://wavebourn.com/images/audio/ps_bb.gif)

http://wavebourn.com/images/audio/ps_bb.gif

Here is schemo of power supply (screen grids' and preamp regulator)

(http://wavebourn.com/images/audio/pyramidps.gif)

http://wavebourn.com/images/audio/pyramidps.gif

However I could use  Zener diode, but 0A2 looks cool and visually indicates presence of a voltage

Also, it looks nice in darkness...

(http://wavebourn.com/images/audio/wavebourntubepp.gif)

http://wavebourn.com/images/audio/wavebourntubepp.gif

I will have another version: 4x 6L6GC per channel in relaxed mode, for 50W only per channel, with smaller output transformers for better clarity of details.

Tolly, you do EXCELLENT fabrication work. I can't WAIT to see your version of a 100 watt AM phone transmitter.

Thank you Joe!

I have an idea about screen modulated couple of GU-50 toobs, with AF feedback from antenna output. I'll try it later when my audio business is up and running.

GU-50 is an interesting toob. Can you tell me what this guy is doing?

http://news.cqham.ru/articles/detail.phtml?id=558

Yeah! LS-50 was developed by Telefunken for Hitler. Russian engineers took it from enemy and made own version GU-50.
It is very linear ray pentode and excellent both for audio and radio.

The guy on your link builds linear amplifiers using GU-50 tubes.

On his page he is standing near his Uragan-1 gear that had not been finished because authorities thought the he can't use GU-43 tube that may give 2 KW of output power so it could be technically possible to break the rules despite the power tranny is up to 1 KW only!

Uragan-2 is an amp made of mobile military transceiver R-140

Cube is amplifier with GU-74 output

The rest is amplifiers with GU-50 outputs.

Polew 4GU50 - 150-200W output FM, 650W SSB

3GU50 "Hi-End" - up to 450W SSB

2GU50 - 250W peak SSB

Is it better?

(http://wavebourn.com/images/audio/gu50red.gif)

http://wavebourn.com/images/audio/gu50red.gif

Here is it with a mirror between hot toobs and transformers.

(http://wavebourn.com/images/audio/gu50red_2.gif)

http://wavebourn.com/images/audio/gu50red_2.gif

Chassis reminds me of a small block chevy.......from the '60s

Was it red?

It is Joe's idea about red color.  ;D

I'm sure you were planning to paint it red all along.

I like the "muscle car engine look" too. The "ignition key" is a great idea. Maybe you can find an excuse to run some heavy cable on top of the chassis (suggestive of ignition wires). Also maybe think about bringing some caps up top next time.

And how about a meter set up to suggest a tachometer, chrome trim ring, a red line, etc.

4X807 instead of 2xGU50 would defenitely need ignition cables.  ;D

I really like the thumbnail indicator tube avatar!!

Thank you!  ;)

Here is it with a front panel with ignition key:

(http://wavebourn.com/images/audio/gu50red_frontpanel.gif)

http://wavebourn.com/images/audio/gu50red_frontpanel.gif

Hey Tolly, I do some repair work for a local music house nearby. I'm toying with the idea of building a neat guitar amp based around an 829B, (There is a Russian equivalent but the number escapes me) I figured I could get ~45-55 watts out in AB1. I may consult with you on this when I get the project up and running. BTW, Walnut Creek is my old stomping grounds. I was station at Mare Island, Vallejo when I was in the Navy.

Hey cut away a little of the spark plug boot and run packard 440 wire, with spark plug boots. The high voltage lead will contain the high frequency transients to the inner conductor thus improving high frequency response. I know packard 440 wire in my big rig gives me that spank second gear feeling.
There must be a marketing angle here somewhere.

You are welcome Mike!

Use GU-50, it is better than GU-29 for audio frequencies!

Wavebourn,

I like the old fashioned tube regulator. Variations on this circuit have been published all over including in the Handbook. I have made them with 6AU6 / 12AU6 error tubes and single 6AQ5's, 12BY7's, 6CL6's, triode connected for up to 120 mA. This is usually just the ticket for a VFO or circuit that wants a little more than what a single voltage regulator tube can do.

The filaments must be isolated (floating) because the tubes are operating quite a bit above ground. A small fill transformer works.

With a pot for R1 and R2, you can make a dandy 100 - 250 VDC supply.

Mike WU2D

Thank you Mike; I have nearly the same but cheaper (my FETs instead of your tubes), though a gas discharge regulator is still used. It serves an indicator's purpose as well,

I recently bought bunch of Russian SG-2S, SG-3s, SG-4S regulators. Some glow orange, some glow pink... Nice!  ;)

I have a few odd regulator tubes from test gear. Some of these are filled with lets just say "rare" gasses and compunds that you would not want to come in contact with. Many unusual performance enhancements could be had through lacing these tubes with radio active trace elements. 

Mike WU2D

Mine contain argon, neon, helium. Innocent neutral gases.

Mike,
       that regulator circuit looks like the one from ny 1963 arrl handbook, except that they used 807's for the cathode follower / pass regulators. I have a very similar circuit for the screen regulator in my 4X1 transmitter.

                                         The Slab bacon

I use one on a command transmitter where the VFO is drawing power. Add the final's screens and you really need more current than you can do with a raw VR tube. The interesting thing about the circuit is about anything can be made to work as a pass device as long as it has the current rating and you can parallel up tubes. It is lEEEENEEEAR however and they do get warm. But who goes around squeezing hot 6AQ5's anyway?

Mike WU2D