Tube AND transistor amp?

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gmoon6 years ago
Re-design wrote what I would have--you can easily sink $150 into the transformers alone for a decently powerful tube amp. Tubes are still the "gold standard" of guitar amplification, but tube amps aren't cheap.

If you must introduce tubes to your signal chain, then why not try a low-voltage "starved plate" tube preamp, like the Valvecaster? And use that with an existing SS amp.

Here's a great link for the project at diystompboxes. Warning: it's a popular DIY project, so that forum link is 118 pages :O at this writing...
arhodes18 (author) 6 years ago
Thanks guys!
I actually found 3 different boxes full of parts that are mean to rebuild an old radio or something of the sort. It has one tube several transistors, resistors, light bulb, small transformer, speaker, and antenna setup for a radio etc. So Im pretty sure I have all the right parts. I just wanted to make a very small amplifier to amplify an ipod or something of the sort. I intend to leave the tube in full view just because of the way it looks. If I do not have what I need for this project, I still want to do something with these parts, I just don't have any other ideas.
arhodes18 (author)  arhodes186 years ago
Forgot to mention it also has a few potentiometers.
Re-design6 years ago
I've built several tube amps and transistor amps for guitar and hifi use.

The main expense in a tube amp it the darn transformers. High voltage and output transformers are heavy and expensive. Mine are usually about half the cost of all the rest of the parts put together.

Transistor amps have much less expensive transformers and this helps with the cost.

My suggestion would be that if you really want the tube sound and mystique just bite the bullet a buy one of any on the nice 15 - 20 amp versions starting about $300.

If you really have just lucked into a junk box full of the correct parts the go for it but if you don't have a schematic in mind yet, how do you know that you have the correct parts?
orksecurity6 years ago
Been done. What about it?
arhodes18 (author)  orksecurity6 years ago
I was just hoping to get a schematic or something similar. And just any how to info. Thanks!
Well, the trivial answer would be to use a tube preamp stage and transistor amplifier, or vice versa. Start with schematics of existing amplifiers, tease apart those stages, cross-connect the signal paths.

The detailed "how to" is a course in analog circuit design.

Of course the other question is "why". There are reasons for using tubes in some kinds of effects boxes, because when over-driven they distort differently than transistors do, and while it's possible to get the same effect other ways some folks are used to the behavior of the tubes -- which is why some electric guitarists insist on tube pre-amps. There are also audiophools who insist that they can hear the difference even when not overdriven -- though lots of experiments with serious double-blind testing have demonstrated that they really can't. So the first question before you do ANY design work is going to be what you hope to get out of the project, and why all-transistor or all-tube doesn't do it for you.
arhodes18 (author)  orksecurity6 years ago
awesome! thank you!

I want to do it mainly because I play electric guitar so the tube is almost just a cool symbol as much as anything. They look AWESOME as well, I love the way they look. so I guess its almost just nostalgia. The reason for not going all tube is to save money because transistors are typically cheaper and use less power, so it would save me a little cash. The power consumption isn't a huge deal, but Im a broke college student and just happened to stumble upon the correct components to make the tube/transistor circuit. So to avoid spending unnecessary extra money I want to use what I have. Lastly I enjoy a challenge, and it will be fun to try to figure this out.

So another quick question, should I find a transistor amplifier circuit and change out the pre amp transistor with a tube circuit?