UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Building a little practical audio amplifier for experimentation

Miguel Lopez · 8th Mar 2019, 5:19 pm

Hello everybody

I want to share with you the steps on building a little and practical audio amplifier, based on Soviet valves. I decided to build this little device in order to use it as a tool in future experimentation on valve electronics. I have always planned to build a radio using valves, but in my modest opinion, first it would be very useful to have a little and compact amplifier to amplify the signals if I'm able to tune and detect them.

The circuit in question is the one which attracted my attention to vacuum electronics about 7 years ago. In that moment I tried to build it but things went improving, knowledge too, and I finally ended building a bigger stereo amplifier which is currently in use at home.
See: https://www.vintage-radio.net/forum/...t=77762&page=6

I've been a bit distanced from vacuum electronics in the last couple of years due to time availability, but I think that now I can resume my experimentation (and fun) playing with glass and electrons, so I decided to go for it.

Anyway, I will make some variations of this circuit as I want to use a vaccum rectifier. All of the valve-based circuits that I have built, have silicon rectifiers, but I'm interested to use a vacuum full-wave rectifier to experiment with the behaviour of this kind of power supply. Problem is that I also want to use a transformer that I winded for another project (to save time and labour) which has a single HT winding. Then I decided to use the circuit on Picture #2, which appears on The Valve Wizard page about rectifiers. This way I can have the behaviour of a full wave vacuum rectifier while I have a single winding transformer. I know, I know.....it will not be an "all-vacuum" set but after all, this is for experimentation.......and fun.

The other thing to have into account is: SPACE. Not outer space, but space in my workshop, my bench and my shelves. My shelves are at full capacity of "probably-I-will-never-use" stuff, as it should be on any DIYER workshop, so space is something very important to have in mind. So, I decided to build the chassis in tower style, in order to save space. This will be a very compact (if I can say so) audio amplifier with a built-in speaker..............

Oh! I forgot to tell you that it will have a built-in speaker. Well, for the same considerations of space and usefulness, I will not use a separate speaker but I will insert it into the chassis too. As the chassis will be build on steel plate, which is not good for a speaker cabinet, I will try to build a small wooden cabinet for the speaker inside the steel chassis. What I have done in the chassis can be seen on Picture #3.

8th Mar 2019, 5:19 pm	#1
Miguel Lopez Heptode Join Date: Dec 2011 Location: Mayabeque, Cuba Posts: 617	Building a little practical audio amplifier for experimentation Hello everybody I want to share with you the steps on building a little and practical audio amplifier, based on Soviet valves. I decided to build this little device in order to use it as a tool in future experimentation on valve electronics. I have always planned to build a radio using valves, but in my modest opinion, first it would be very useful to have a little and compact amplifier to amplify the signals if I'm able to tune and detect them. The circuit in question is the one which attracted my attention to vacuum electronics about 7 years ago. In that moment I tried to build it but things went improving, knowledge too, and I finally ended building a bigger stereo amplifier which is currently in use at home. See: https://www.vintage-radio.net/forum/...t=77762&page=6 I've been a bit distanced from vacuum electronics in the last couple of years due to time availability, but I think that now I can resume my experimentation (and fun) playing with glass and electrons, so I decided to go for it. Anyway, I will make some variations of this circuit as I want to use a vaccum rectifier. All of the valve-based circuits that I have built, have silicon rectifiers, but I'm interested to use a vacuum full-wave rectifier to experiment with the behaviour of this kind of power supply. Problem is that I also want to use a transformer that I winded for another project (to save time and labour) which has a single HT winding. Then I decided to use the circuit on Picture #2, which appears on The Valve Wizard page about rectifiers. This way I can have the behaviour of a full wave vacuum rectifier while I have a single winding transformer. I know, I know.....it will not be an "all-vacuum" set but after all, this is for experimentation.......and fun. The other thing to have into account is: SPACE. Not outer space, but space in my workshop, my bench and my shelves. My shelves are at full capacity of "probably-I-will-never-use" stuff, as it should be on any DIYER workshop, so space is something very important to have in mind. So, I decided to build the chassis in tower style, in order to save space. This will be a very compact (if I can say so) audio amplifier with a built-in speaker.............. Oh! I forgot to tell you that it will have a built-in speaker. Well, for the same considerations of space and usefulness, I will not use a separate speaker but I will insert it into the chassis too. As the chassis will be build on steel plate, which is not good for a speaker cabinet, I will try to build a small wooden cabinet for the speaker inside the steel chassis. What I have done in the chassis can be seen on Picture #3. Attached Thumbnails __________________ When electrons move, things happen. There's nothing you can do that can't be done.