There’s a mystique among both audiophiles and musicians about vacuum technology, thus having a tube amp still carries a bit of a cachet. New ones can be bought for eye-watering prices and old ones can be had for the same price with the added frisson of unreliability. Happily it’s surprisingly straightforward to build your own, as [_electroidiot] shows us with a fairly inexpensive build.
The design is inspired by the guitar amps of the 1950s and 1960s so it’s not for audiophiles. The circuit is a pretty conventional single-ended one with a two stage double triode preamp and a single power output tube. The transformers are usually the difficult part of a build like this one, and here instead of resorting to using a mains transformer for audio they come from a defunct 1960s Phillips radio. We especially like the old-school construction technique with a folded aluminium chassis and liberal use of tag strips on which to build the circuits.
The result is something that would have been in no way out of place in the 1960s, and proves that tube circuitry isn’t beyond the constructor in 2023. If it’s whetted your appetite for more, we can help you there.
That looks like something my late dad would’ve built :)
I feel the word late here… seems a little macabre.
meh…. it’s better than ‘dead’ 🤷♂️
You’re the guitarist for Live?
The cost drops further if you use a 6SL7 in place of the 12AX7. The 6SL7 is electronically the same as the 12AX7, except that the filament voltage is a simple 6.3 volts and audiophiles haven’t driven the price through the roof. The 6SL7 is also an octal, so it looks cooler too. There are a couple of ways to go with inexpensive finals. A 6AQ5 is really a 6V6 (think Fender Princeton) in a mini envelope. If the 6AQ5 isn’t enough power, consider a 1625. The 1625 was made on such a scale in WW2 that you can find them still in the box for under $10 on eBay. This tube is basically an 807 with a 12 volt filament.
I built an inexpensive single-ended amp with a 6SL7 driving a 1625 (housed in wood salvaged from an old dynamite crate). For the output transformer, I used the vertical transformer from an old color TV. Yes, it’s not an audio transformer, but it’s designed for AC amplification with steady DC flow, it was $3 NOS, and it actually works (maybe I got lucky with that model). My junkbox had some gas regulator tubes that I used for the screen supply, and I like the glowing purple when they operate. Screen bias is 300 volts with 400 on the plate, though you could go up to 500-700. This amp fills a room. My main regret is going quick and dirty on the tone. The 2-knob circuit that I copied from somewhere was easy and cheap, but it leaves a lot to be desired.
Heathkits didn’t have a tone control on their mono block amps. They used a preamp. You could do the same.
You make an excellent point! I love my McIntosh MC-50 (even though it’s solid state. It doesn’t have any tone control, either.
So, are you really a McIntosh? Of the audio fame?
I’m not being snarky, just curious.
Yes, I’m really a McIntosh, but with no connection to the audio company. The MC-50 sort of fell into my lap. A coworker’s mom had been selling of some McIntosh gear now and then, and they would ask me to verify function. Though I have always wanted a piece of McIntosh equipment, the solid state didn’t grab me until I saw this amp.
That’s what I built, based on the first 5w Fender amp.
Schematic?
Let me see if I can find it. I built this about 15 years ago. The 6SL7 portion was taken straight from a Fender Princeton. https://photos.app.goo.gl/s1GeHb4pyHgWrJKi8
Just a word of caution: don’t trust transformers salvaged from tube radios. They are six or more decades old, were designed to run hot with normal usage, most of them have been overloaded until they began to stink at least once in their life and the insulation material will be severely deteriorated. Better connect ground/chassis to protective earth and use a RCD/GFCI protected outlet to avoid your guitar going live on mains voltage.
I completely agree with you, regarding the earth/ground connection and GFCI. An isolation transformer would be nice too, on the really cheap vintage amps without power transformers, where there’s only an RC pair between the line and chassis ground. I once made the mistake of playing guitar barefoot in a basement with a concrete floor, with one of those.
Transformers can be checked for leakage paths with a Megger, or any megohm meter that applies around 500 V to a device under test (and ideally has a third “guard” lead), easily enough.
Played a fender champ on outside back patio..touched patio door and , wham.
Looks like the amplifier i made whem i eas at school real tubeway electronics we are glass
I Just built a tube guitar amp for my son. I know nothing about guitars I am not a musician nor an audiophile. But I do know a bit about tubes and RF. I have a bunch of 807’s I wanted to do something with and my son talked about tube amps so I built one. I based my design on the Fender Delux 5e3 with PP 6V6’s but substituted the 807’s as it turns out it ended up being a Fender Pro 5e5! The Pro 5e5 uses 6L6’s which is characteristically the same as the 807 (and the 1625).
When my son tried it out his jaw dropped and his eyes went wide! “That’s the sound I want to get”…., “it’s just like Paul McCartney’s in Hellter Skelter!” . The base was very deep and full. The high’s were very clear. The distortion he wanted was perfect.
So if anyone’s thinking about a Guitar tube amp with 807’s, go for it, they work great!