GE "Dual Speaker" radio to Harmony H303 conversion : Help, please?

[Spasticteapot]

Originally posted by ThSpeakerDude88
Thanks I'm glad you like it! It was actually thrown together, and then later spiffed up. I never planned on it turning out the way it did . Actually my next amp is more art deco. Please be aware that I build these and sell them to people, so change the design around a bit ( IE, don make it look exactly like it. ) I took designs from a BUNCH of different amps and mixed them all into one. Look at some older gibson amps ( 1940's stuff). Also supro, valco, oahu, kay, harmony etc. They were all off-brand amps but all were very art deco looking. If you have seen Swart amplifiers design it is based almost exactly off of a late 40's harmony.

On another note: They dont specify 40uf and 60 uf, they specify 40 and 20. This adds up to a total of 60uf right off the rectifier, and then there is an RC filter for the preamp and grid. You can add as many caps as you want to a string of RC filters, as long as right off the rectifier there is no more than 60uf ( this is usually true for all tube rectifiers) and there is a resistor after that.

Well, dang. I suppose you're right.

I just got an isolation transformer rated at 50w, which I think should be adequate for a 2w amplifier.

After this, I'm thinking of building something REALLY loopy - a 2w amplifier based off of subminiature tubes. I'm currently pondering how I can most easily build a 280 volt power supply to power it.

[ThSpeakerDude88]

Look at Z-vex's stuff.

As for the power supply, I personally would use a switchmode power supply. Small, high power, and easy to rectify. Only problem is you have to use adequite shielding or you have problems with RF interference, especiall with guitar. However, if you are looking at less than 250mw of power (1/4 watt) I am sure that a 12v 1.5 amp wall wart and a 12v 1 amp xfrmr in the chassis wired back to back would work fine. However, for the cost you cant go wrong with the one I ordered for the model two. http://www.tubesandmore.com/scripts...P?item=P-T262E6

It is very small, and you oculd squeeze 3-4 watts out of it just fine. It wouldnt even break a sweat with submini's.

[Spasticteapot]

Originally posted by ThSpeakerDude88
Look at Z-vex's stuff.

As for the power supply, I personally would use a switchmode power supply. Small, high power, and easy to rectify. Only problem is you have to use adequite shielding or you have problems with RF interference, especiall with guitar. However, if you are looking at less than 250mw of power (1/4 watt) I am sure that a 12v 1.5 amp wall wart and a 12v 1 amp xfrmr in the chassis wired back to back would work fine. However, for the cost you cant go wrong with the one I ordered for the model two. http://www.tubesandmore.com/scripts...P?item=P-T262E6

It is very small, and you oculd squeeze 3-4 watts out of it just fine. It wouldnt even break a sweat with submini's.

I just ordered a 50va isolation transformer, but for the submini tube amp, I'm looking to go with battery power. I'm thinking of using a small flyback transformer setup, but finding transformers rated for 50khz is kind of hard.

[ThSpeakerDude88]

try the car audio section of this site, they will be able to help you better. For something like that you would use a small ferrite core. A 1 inch core would be good for 50 watts or so, very small. Theoreticly, if you were to only need about 10 watts of power draw, you could use a very small x-frmr indeed.

Batteries won't last long at constant current draw...Think radio controlled car at max speed for about 10-15 minuites on end.

[Spasticteapot]

Originally posted by ThSpeakerDude88
try the car audio section of this site, they will be able to help you better. For something like that you would use a small ferrite core. A 1 inch core would be good for 50 watts or so, very small. Theoreticly, if you were to only need about 10 watts of power draw, you could use a very small x-frmr indeed.

Batteries won't last long at constant current draw...Think radio controlled car at max speed for about 10-15 minuites on end.

Rechargable NiMh "D" cells are rated for 10 amp-hours at 1.5 volts. Five of them in series, giving me ~6V, would mean a grand total of 75 watt-hours.

Assuming an efficient buck-boost or flyback power adapter, that would leave me at least five hours on a charge.

[ThSpeakerDude88]

This is true, however in practice run times rarley work that way. This is due to the fact that music varies so much in voltage and current output. I was assuming you were going to be doing class A, where your batteries would not last long at all. However I went back and re-read your post and saw you meant AB1. This will last longer, because READ: Properly used, tubes are very efficient in converting available power to output. HOWEVER! it is their heaters that make them inefficient power wasters. In a typical 20 watt guitar amp, including all the preamp tubes and reverb and teremelo, you are wasting over 20 watts of power just in the heaters!

[Spasticteapot]

Originally posted by ThSpeakerDude88
This is true, however in practice run times rarley work that way. This is due to the fact that music varies so much in voltage and current output. I was assuming you were going to be doing class A, where your batteries would not last long at all. However I went back and re-read your post and saw you meant AB1. This will last longer, because READ: Properly used, tubes are very efficient in converting available power to output. HOWEVER! it is their heaters that make them inefficient power wasters. In a typical 20 watt guitar amp, including all the preamp tubes and reverb and teremelo, you are wasting over 20 watts of power just in the heaters!

I suppose you're right. However, this amplifier uses ridiculously tiny tubes, specifically the 6112 dual triode and the 5902 pentode (yeah, it's running in class-A.)

http://jonanderson.mn.googlepages.com/

The amplifier is going to be very, very, very small - in fact, not too far off in size from the Z.Vex amplifier that you linked me to.

That said, after adding up the cost of tubes (about $20 shipped), vibrator (about $20 shipped), and output transformer (about $35 shipped), I've decided that, unless someone else is paying me to build it, I'm better off converting an old battery-powered tube radio instead.