50 yr Old 3 tube amplifier circuit?

[gary350]

Does anyone remember the old 3 tube amplifier circuit that used a 50C5, 35W4 and ???? what was the other tube...........12AT6 or something like that?

Does anyone have this circuit?

I already did a web search there are 100s of old tube circuits but not this one. It was never a great amp but it was a fun project for the beginner.

 

[cowboybob]

More likely a very simple radio. Although, by ignoring the detector side, could have been an amp.

35W4 was the rectifier, 12AT6, 12AV6, whatever, diode detector, triode preamp with a 50C6 final amp.

Want to repair it, or what? A zillion of those types of devices were made, by everybody...

Simple amp like that, especially with no power transformer, you ought to be able to trace out a schematic. Component values should still be visible and, frankly, were pretty sloppy back then.

 

[KeepItSimpleStupid]

How about: **broken link removed**

 

[gary350]

ote="KeepItSimpleStupid, post: 1166109, member: 158325"]How about: **broken link removed**[/quote]

That is it. There are several versions of this 3 tube amp this circuit is the closest one I have seen so far to the circuit I built and experimented with in high school, the one I experimented with had a 12AT6. T1 is 5K and 8 ohm.

One version has a tone control circuit between the 12AX7 and the 50C5, I built this one once. There is another version with a tone control circuit between the 50C5 and the audio transformer.

There is one version that uses both halves of the 12AX7 so the amp has 2 inputs like microphone and turn table.

There is also a newer version that uses a bridge rectifier in place of the 35W4 and two 50C5 tubes in push pull with the 12AX7.

I was day dreaming about how much fun I use to have building stuff every day after high school. I had a small work bench and I lived to build projects and experiment. Now that I am retired I need to get into this again just for no other reason but to have fun. I want to build a 6AQ5 push pull amp and 6BQ5 Dynaco 35 amp.

 

[Nedix]

Beyond the quality of the sound, gain and other parameters, I think the best feeling is when one sees the "magic eye" working. Waiting for the filaments to warm up, the AFC going wild along with heating of the tubes, the static ... that's poetry

 

[DWFrancis]

Here is a schematic for a related circuit out of a GE Tube Handbook

 

[gary350]

This is the very first amplifier I ever built 1967 it was a great learning experience and FUN. It is basically a useless amplifier but I want to build it again. There are several slightly different versions of this circuit. V1 is 12at6 or 12av6 or others. One version has a current limiting choke coil in the heater circuit. T1 is 5K ohm, 8 ohm. One version has 2 inputs, mic and phone. This is not 5W like the circuit suggest it is about 2W depending on the V1 tube. 14GT8 was never 1 of the tubes in the original circuit so maybe this circuit really is 5W.

**broken link removed**

 

[cowboybob]

Welcome to ETO, DWFrancis!

Very nice, classic 3 tube , mono, Class AB audio amp. The veritable 12AX7 was the work horse dual triode pre-amp/mixer/driver of choice in the 1950-60s. Also classic beam pentode 35C5 finals. Loved the transformerless use of direct wall AC (always a low level 60Hz hum at full volume!).

Did not mind waiting for the filaments to heat up.

 

[DWFrancis]

Here are two more transformer-less designs, this time from the RCA RC-30 Receiving Tube Manual. (1975)

The mono amp uses a 50EH5 and the stereo amp uses a pair of 60FX5's. The recommended output transformer for both is a Triad S-16X. (3000 ohm to voice coil) Just looking online for these, I'm starting to think transformer-less output would be much easier on the budget...

Either one of these might be a fun project.

(There is also a nice 8 Watt, 6EU7-6AV6-6L6-5Y3, schematic in the same manual, but it needs transformers at both ends and a Gibson ES-335 to plug into the microphone input!)

 

[audioguru]

I think you should kiss it goodbye, bury it and move on.

 

[gary350]

Here are two more transformer-less designs, this time from the RCA RC-30 Receiving Tube Manual. (1975)

The mono amp uses a 50EH5 and the stereo amp uses a pair of 60FX5's. The recommended output transformer for both is a Triad S-16X. (3000 ohm to voice coil) Just looking online for these, I'm starting to think transformer-less output would be much easier on the budget...

Either one of these might be a fun project.

(There is also a nice 8 Watt, 6EU7-6AV6-6L6-5Y3, schematic in the same manual, but it needs transformers at both ends and a Gibson ES-335 to plug into the microphone input!)

Those circuits are in the back of the RCA tube manual. I built the 8W amp for 1st year college electronic lab class project. The teacher ran the amp through several tests he said it is one of the best circuits he ever saw it checked out excellent on the scope. I got A+ on the project. I think the 8w amp will be more useful and more fun than the 2W amp.

 

[schmitt trigger]

Here is a schematic for a related circuit out of a GE Tube Handbook

The very first circuit that I built that actually worked, was this amplifier.

The 35C5 tubes were far more difficult to find that the 50C5, so I used them. To not to exceed the available 117 volts, I removed the 35W4 and substituted it with a selenium rectifier like this one:
http://tikalon.com/blog/2013/selenium_rectifier.gif

You are right....nothing reminds me more of my youth than the loud 60 Hz hum and the pops and scratches of the vinyl record.

 

[gary350]

The very first circuit that I built that actually worked, was this amplifier.

The 35C5 tubes were far more difficult to find that the 50C5, so I used them. To not to exceed the available 117 volts, I removed the 35W4 and substituted it with a selenium rectifier like this one:
http://tikalon.com/blog/2013/selenium_rectifier.gif

You are right....nothing reminds me more of my youth than the loud 60 Hz hum and the pops and scratches of the vinyl record.

If your tube amplifier had 60 Hz hum then it had a bad power supply capacitor.

**broken link removed**

 

[KeepItSimpleStupid]

If your tube amplifier had 60 Hz hum then it had a bad power supply capacitor.

How true.

 

[alec_t]

Hum could also be introduced via the tube heater supply.
Sign of the times, how resistance values are expressed in that schematic. Either that, or the letter 'k' was non-functional on the author's typewriter .

 

[Nigel Goodwin]

Sign of the times, how resistance values are expressed in that schematic.

Sign of the country as well

 

[gary350]

Hum could also be introduced via the tube heater supply.
Sign of the times, how resistance values are expressed in that schematic. Either that, or the letter 'k' was non-functional on the author's typewriter .

Sign of the times, Same thing for batteries these days. 3000 ma battery sounds bigger and better than 3a. I think this is a form of deception to trick people that don't know any better. Many people would rather have the 3000000 ua battery.

 

[KeepItSimpleStupid]

And don't forget all of these mm things, like 630 mm long.

 

[schmitt trigger]

Sign of the times, how resistance values are expressed in that schematic. .

Signs of even older times, when picofarad capacitors were labeled micro-microfarads, and hertz were labeled cps (cycles per second).

And a 5% resistor was considered semi-precision.

 

[gary350]

I found a gold mine today. I was driving along the road and there was a TV laying off in the grass. I drove past there 3 times in the pasts 2 weeks the TV was still there. Today I saw the TV again then I remember I needs a speaker plug for a yard sale item so I stopped to get the TV hoping it will have the part I need. It was a 1970 TV with power transformer, audio transformer, choke coil, lots of good resistors soldered point to point between terminal strips. Good capacitors and hook up wire too. This might be just what I need to build this 8 watt amplifier just have to wait and see. When I have time I will check the power transformer to see if it is what it I need 300-0-300 with 5v and 6v with CT would be a miracle find. I still need a speaker plug.