Depends on what you want to spend, what topology desired, power, and what sort of speakers you are using.

You can go for either a rebuilt vintage offering on eBay, or a used newer commercial amp, or the newer chinese amps that get pumped on there.
Don't forget about Audiogon, though more catered to boutique gear.

If you want to go for a vintage tube amp to rebuild and learn about vacuum tube circuits, put the most concern into the output transformers.
A good tube circuit is only as linear as the output transformer, unless it's a OTL or something....
The OPT's make or break a circuit.....IMO.

The Dynaco ST-70 is a 35 wpc push-pull using EL-34 output tubes, they made like 300,000 of the things over a 30 year period or something like that.
The main reason the Dynaco ST-70 is such a classic amp is the OPT's, they measure excellent.
They always pop up on eBay in various conditions and prices. If one were to go with a Dyanco, go for a stock ST-70 to rebuild yourself.
Then you don't have to deal with someone's cobbled up rebuild, or goofy modifications or other crap, and the price will be lower possibly.

The internet is saturated with info, mods, schematic, even the assembly manual is online.

Dynaco made quite a bit of stuff, the Mark III 6550 push-pull mono amps being the higher output offering.

95honda has a nice clean stock example of a Dynakit ST-70, with the brown cage the earlier versions had.
More than likely the OPT's have cloth leads, indicative of being made in the USA, and more desired. The plastic leaded OPT's of the newer versions are supposed to made in Japan, but are a fine output tranformer nonetheless.(I think...) :shock:

Other options are the HH Scott integrated amps. Though as a integrated amp, it is a more complicated circuit.

Eico has some rather simple vintage integrated and power amps, but they are starting to get way overpriced for what they are. Most use good output transformers.

A vintage Magnavox tube amp from a console can be made to look good with some work. Not much powerwise but they sure sound damn good.
I have a singled-ended 6BQ5 version, and a 6BQ5 PP maggotbox, they made 6V6 versions with the older console amps.

There is quite a bit of vintage tube amplifiers brands out there, ranging from absolute shit to shit we'll never see or afford.

You may find something local living on the west side,(yard sales, classified ads..).
There is more interest in vacuum tubes over there than over here.

You could buy a tube amp in kit form, but it all depends on how much cash one wants to throw out for decent quality.

You can scrounge up some test gear, a good 500 volt/200 milliamp tube DC power supply, build a breadboard jig and get deep.......

I'm trying to follow through on mono EL-34 PP amps, using the PS transformers, output xformers and the chassis of a pair of Lowery 6550 PP mono organ amps.
I'm slow.......

Mike

One thing with vintage tube amplifers is most use multisectional electrolytic capacitors, some axial paper 'lytics, and carbon comp resistors.
They also use various forms of bi-polar coupling caps, which can leak DC over time, you don't want that on the grid of a tube meant for AC signal levels.

Depending on the vintage of the unit, the parts can be 40 years old or better. The electrolytics can (some can't) be re-formed and live longer with no real issues, but fresh capacitors are the best option for the long term.
Carbon composition resistors can drift over time, and moisture doesn't do them much good.
This is mostly with 1/2 watters, the one and two watters seem to hold their value better. But they sound warm and yummy......so they claim.

I guess I'm saying the chances of the tubes still being strong and useable are greater than the caps and resistors being within tolerance.....
Simple checks with the PS xformers, chokes, and output iron for shorts and known resistance/impedance are things to keep in mind.

It's just a matter of checking tolerances, replacing what's bad, and checking voltage and bias once everything is up and going. A guy can do it with just DMM, I guess.
Can't re-form a capacitor, just replace it.

Mike

That one for 51 bucks is pretty much a basket, the output transformers appear to be a bit rusty, but they should be ok....you don't know until you have them on the bench....

The underside pic of the amp has no power supply xformer, but other pics show it? Makes one wonder if the PS transformer may be toast, or you just don't get one.

Uh...one thing about the ST-70, the PS xformer's were underated, they won't outlive the OPT's.

The output transformers I think fetch around fifty bucks or so.....it's a take a chance auction.

The auction with Curcio upgrade driver boards at a 450 BIN has rather nasty layout IMO. It may be quiet, but it doesn't look too special.
Overpriced to me, and you deal with someone else's mess.

The near mint ST-70 at 203.50 looks like a nice clean plug and play amp there, and he doesn't mention modifications...though one should ask the seller.
It might hit 400,450 bucks. Who knows, eBay always amazes me.

Now you got myself lurking fleabay for vintage tube amplifiers.....not a good thing.....

You made it. Welcome!

Always good to see new people..  Welcome!

Nice isolation feet What are those?

Double post......I keep getting blasted off the site...argh...