been away from the bench for some years, i had a good few threads in the radio section back then regarding pantry transmitters 😉
I'm looking to dig out the box of valves again and mess with simple audio amps, mostly for educational reasons, basically i like playing with valves 😉
Seems the hardest struggle i face is the output transformer - is there an item you could recommend that will allow the widest scope of playing about - different valve types and designs etc ?? They seem to be hideously expensive so i wouldn't want to buy more than one or two 🙂
I have various power supply transformers, tons of valves and components but the OPT is a struggle.
Hammond do a configurable transformer, with half a dozen taps on it, there's a push pull and single ended variant. Only good for a couple of watts, but great for playing around with.
Yes from Australia but don't let that put you off. AU$1 = 55 GB pence so halve the price, roughly.
Here is the amp I designed using it. The EL84s are driven by cathode followers so as to not pump up the bias when driven into clipping. It clips cleanly when overdriven, unlike most other designs. If interested I can post the power supply design too, but I thought this might be the basis of a few ideas.
You might be able to find a similar PA 100v line transformer from a more local source, but I can vouch for this one.
BTW, PA line transformers can only be used unmodified with push-pull amps. For single ended use, you can restack the core so as to get a suitable air gap.
Yes from Australia but don't let that put you off. AU$1 = 55 GB pence so halve the price, roughly.
Here is the amp I designed using it. The EL84s are driven by cathode followers so as to not pump up the bias when driven into clipping. It clips cleanly when overdriven, unlike most other designs. If interested I can post the power supply design too, but I thought this might be the basis of a few ideas.
You might be able to find a similar PA 100v line transformer from a more local source, but I can vouch for this one.
BTW, PA line transformers can only be used unmodified with push-pull amps. For single ended use, you can restack the core so as to get a suitable air gap.
Thanks, that looks useful - there is a bit clipped off the input side, do you have a better file of it please??
Hammond do a configurable transformer, with half a dozen taps on it, there's a push pull and single ended variant. Only good for a couple of watts, but great for playing around with.
The cheaper one is more versatile , just be careful with the max current of 40ma is not overloaded. Very much like the ones referred to by Sam that were always in the workshop spares cupboard.
I was not sure what you were after, thought it was push pull type. Still the links led you to other transformers.
Transformers are the bugbear in these cases. It's why I never brought my junkbox amp to the bench. Without cannibalising something else, I have nothing to build upon, though a member did suggest a transformerless design. I guess being a bit more of a traditionalist, I'd prefer a conventional design.
Keep an eye on eBay, they sometimes come up on there, and just right now, one seller is offering a few used mains input and audio output transformers (one of each as a set) for basic amp builders.
I think this one is probably the best option in the end - its UK made, a good match for an EL84 build and although a bit pricey it has a good amount of iron in it unlike some of the tiny chinese variants...
Look very well made, I wish they would put a postal address on their website. Any way found the address on the Made in Britain web site, they are in Chichester.
Have found a little Mullard two valve circuit that looks good for messing with,
That is the famous Mullard 3-3. I wouldn't bother messing with it....it sounds very very good as it is. Not hi fi in the true tradition I suppose but gives an extremely good account of itself with a decent speaker and output transformer. I've built three of these in the past. One of them was as an ordinary record player amplifier. It was so good, I fitted external speaker sockets and built another for stereo.
