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Amplifier Recommendation

Ron Brown

Ron Brown

Cultosaurus Erectus
I know tube radios (receiver, transmitter, transceiver) pretty well from the amateur radio perspective, but don't know a great deal about tube amplifiers. I currently have a little 50 WPC tube hybrid for the stereo, but I'm looking to go full tube to pair with a Nikko STA-7070 and ESS AMT 1aM speakers.

So, what recommendations can you offer for a relatively inexpensive, entry-level tube amplifier? I'm probably looking for > 25 WPC output. It doesn't have to be vintage, but I would prefer that.
 
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What is the budget? Right off the top of my head I would say a nice restored Dynaco ST-70. They pop up here in barter town usually at reasonable prices.
Some reasons why I suggest this amplifier is they have never gone out of production by one company or another and there is tons of documentation and support for them along with a long list of modifications, if you wish to take that route. These amps are 35wpc. Here is a picture of mine I had setup in a second system for awhile, its on the far right.
 

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Lavane said:
What is the budget? Right off the top of my head I would say a nice restored Dynaco ST-70. They pop up here in barter town usually at reasonable prices.
Some reasons why I suggest this amplifier is they have never gone out of production by one company or another and there is tons of documentation and support for them along with a long list of modifications, if you wish to take that route. These amps are 35wpc. Here is a picture of mine I had setup in a second system for awhile, its on the far right.
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That was my first thought in diving down the amplifier rabbit hole, but I wanted to get some recommendations from people actually using the equipment. The Dynaco seems to be pretty popular and there's a reason for that. Thanks.
 
ceylon said:
maybe its because i comwminto hifi from pro audio, but really like a volume knob on an amp.
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I omitted the stereo/mono switch and put a volume control in its place. When using a preamp, I just run the volume control at full. But I have used the amp stand alone with a selector for line level sources and ev2n a stand alone phono preamp.
 
Lavane said:
I omitted the stereo/mono switch and put a volume control in its place. When using a preamp, I just run the volume control at full. But I have used the amp stand alone with a selector for line level sources and ev2n a stand alone phono preamp.
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how does the presence or use of a volume pot affect the input impedance of the amp?
 
It doesn't seem to if left at full with a preamp, or used as a volume control without a.preamp. I have noticed some miller effect when turning the volume control down with a preamp installed though. Most of the SS power amps I've had and have now have gain controls on them. A Magnavox tube amp I modified has an added volume control that seems to work pretty much the same as the ST-70.
 

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You might consider a Scott LK-72/LK-72B. The "B" variant has full bias adjustment which is a definite plus though the LK-72 can be easily modified to provide that feature. The LK-72/B is 35 WPC and uses a tube rectifier which is easier on components on power-up. The output transformers are beefy and the amp has a really great sound, easy to listen to.
 
If you decide to go with a tube preamp along with the amp, an Eico integrated would work well. I’ve had both the ST40 and currently use an ST70.

The ST40 was a sweet amp and only needed a basic recap to get it going very well. I sold it too soon and then got the ST70. That amp took a bit longer for me to tame but once I did I was rewarded.

With a tube integrated you could still use the tuner from the Nikko. But if you are sure you want to keep the Nikko preamp in your rig, the Dynaco would be nice. And if you can live with less power, people love their Dyna ST35 amps.
 
Yep. Dyna ST-70. A humble amplifier introduced over 60 years ago which may well last another 60 with a proper rebuild. I enjoy mine and don’t know what could replace it.
 
Thanks for the information. It looks like an ST-70 is in the cards. It's about what I had decided on, but wanted some recommendations.
 
I'll add another suggestion for an ST-70. I picked up mine almost 4 years ago from a Good Will. It worked fine and appeared to be all original, other than two caps on the board. I replaced all the caps, resistors, and selenium rectifier as suggested on AK. In the past couple years, I used adapters to get away from the really tired 7199's (I still have the original board) and replaced them with 6GH8's. Most recently, I replaced the EL34's with 6CA7's and really like the sound of them. This is a good sounding, reliable, easy to work on amp that looks at least decent.
 
David_NC said:
I'll add another suggestion for an ST-70. I picked up mine almost 4 years ago from a Good Will. It worked fine and appeared to be all original, other than two caps on the board. I replaced all the caps, resistors, and selenium rectifier as suggested on AK. In the past couple years, I used adapters to get away from the really tired 7199's (I still have the original board) and replaced them with 6GH8's. Most recently, I replaced the EL34's with 6CA7's and really like the sound of them. This is a good sounding, reliable, easy to work on amp that looks at least decent.
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That's got to be one of the best goodwill finds I've ever heard of!
 
maxhifi said:
That's got to be one of the best goodwill finds I've ever heard of!
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Absolutely! I almost passed it up, actually! I wasn't familiar with them or tube equipment in general at that time. I looked at it and was like meh. An older gentleman saw me looking at it and kept telling me I needed to buy it. I asked why he didn't, and he said that he already had two and that I should buy it. I tested it for output using a couple random speakers with attached speaker wires; it passed and came home with me. Of course, the fact that four other guys wanted it at that point reinforced that fact that I should buy it.
 
A guy at a local thrift told me that a friend found one at another store I frequent but I’ve never found anything like it at a thrift store.
 
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