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JBEHBA
New Member
General impressions are quite positive for the AU-70. It's a sweet sounding amp that was often overlooked but has been getting more attention lately. I've had mine for about 3 years, and had it recapped 2 years ago. I have the matching TU-70 tuner, and I think it's a hard combo to beat for sound and looks.
I can't comment much on maintainability other than it's a tube amp, and needs to be treated and cared for as such - but will let those who are more knowledgeable than I chime in.
You're correct, the phono state is transistor based, similar to the AU-111. I'm a casual vinyl listener and don't have any complaints from the AU-70's performance. Would probably depend on what your phono reference is.
If it's in good cosmetic and working condition, well-maintained and within your budget, it's a beautiful amp worthy of consideration. And if you pick it up at a decent price and it's not to your liking you should be able to recoup your cost as prices continue to go up.
I can't comment much on maintainability other than it's a tube amp, and needs to be treated and cared for as such - but will let those who are more knowledgeable than I chime in.
You're correct, the phono state is transistor based, similar to the AU-111. I'm a casual vinyl listener and don't have any complaints from the AU-70's performance. Would probably depend on what your phono reference is.
If it's in good cosmetic and working condition, well-maintained and within your budget, it's a beautiful amp worthy of consideration. And if you pick it up at a decent price and it's not to your liking you should be able to recoup your cost as prices continue to go up.
I'll echo the sentiment above with the following caveat: if it hasn't already been restored (all electrolytic caps and paper in oil caps replaced) in which case it will be much more expensive to buy, it will be a fairly difficult rebuild, and owing to its age, will have to be done straight away if you expect reliable performance and longevity from it.
The AU-70 is built on a compact chassis for a tube amp (the AU-111 is physically much larger by comparison) and as a result is not an easy restoration project. Everything underneath is point to point wiring and is very tightly packed in due to the space limits imposed by the "standard" size versus being an oversized unit.
The AU-70 also uses 7189A output tubes which run at VERY high plate voltage. All tube amps contain potentially lethal voltages, but this one runs even higher than most, making working on it even more dangerous than is typically the case. I'd definitely not consider it an amp suitable for a novice to work on.
Gettng one in shape and working right does pay off though and is absolutely worth doing if you don't overpay for the initial purchase of the unit.
The AU-70 is built on a compact chassis for a tube amp (the AU-111 is physically much larger by comparison) and as a result is not an easy restoration project. Everything underneath is point to point wiring and is very tightly packed in due to the space limits imposed by the "standard" size versus being an oversized unit.
The AU-70 also uses 7189A output tubes which run at VERY high plate voltage. All tube amps contain potentially lethal voltages, but this one runs even higher than most, making working on it even more dangerous than is typically the case. I'd definitely not consider it an amp suitable for a novice to work on.
Gettng one in shape and working right does pay off though and is absolutely worth doing if you don't overpay for the initial purchase of the unit.
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Sloper1940
Active Member
Love my AU70.
l havent used the phono stage, use the AUX all the time.
Replaced all the caps, stuffed the cans and replaced diode.
Sent it to a tube expert to do the final adjustments and check it as l had no idea and it scared me a little.
They do run real hot.
regards Bruce
l havent used the phono stage, use the AUX all the time.
Replaced all the caps, stuffed the cans and replaced diode.
Sent it to a tube expert to do the final adjustments and check it as l had no idea and it scared me a little.
They do run real hot.
regards Bruce
The AU-70 does not have pre-out and main-in jacks on the rear panel, so the short answer is no. The long answer is that such jacks could be added in the course of a restoration, making it possible to use the AU-70 as either a preamp or as a power amp (with an outboard preamp feeding signal to main-in jacks). There may be other issues in adding such jacks, related to the loading of existing circuits when the pre and power stages are disconnected. I'm not a tube amp expert, so would caution about making such a mod before properly researching it.
As well, it would seem a waste of the AU-70's capabilities to use it only as a preamp. Probably the strongest point of this model is it's output stage, owing to it's specific output transformers and the 7189A output tubes. It has a "bite" to it's sound which is what has made it popular in the first place. It's control amp section, while perfectly adequate, is not known to be particularly exceptional. If only seeking a high quality preamp to go with the Mac, you may well consider other candidates for the job.
This discussion raises another issue regarding proper restoration: all the RCA jacks and speaker terminals should be replaced. The RCA jacks used in the original build are of an obsolete flared type that does not properly accomodate modern RCA plugs and results in connection issues. The stock speaker terminals are screw terminals really only fit for using zip cord, and if you prefer to use a better grade of speaker cables, will need to be replaced with modern binding posts.
As well, it would seem a waste of the AU-70's capabilities to use it only as a preamp. Probably the strongest point of this model is it's output stage, owing to it's specific output transformers and the 7189A output tubes. It has a "bite" to it's sound which is what has made it popular in the first place. It's control amp section, while perfectly adequate, is not known to be particularly exceptional. If only seeking a high quality preamp to go with the Mac, you may well consider other candidates for the job.
This discussion raises another issue regarding proper restoration: all the RCA jacks and speaker terminals should be replaced. The RCA jacks used in the original build are of an obsolete flared type that does not properly accomodate modern RCA plugs and results in connection issues. The stock speaker terminals are screw terminals really only fit for using zip cord, and if you prefer to use a better grade of speaker cables, will need to be replaced with modern binding posts.
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