2. amps-preamps
  3. 1233757559

Cayin A70T has bogus tube rectification?

I hate starting this thread. I am also a little hesitant because

a.) I bought the amp and hate the thought of its resale value after I post this

b.) I am not an electronics expert, so I have to rely on other experts for the facts.

Here is the basic story. I bought the amp from an audiogon member about a month ago. A friend of mine bench tested it and found a very large amount of crossover distortion on the scope. We unbuttoned the amp to look at the circuit and try and figure out what was wrong - but that is a side issue. The real issue is that there were four diodes strapped to the base of the 5AR4 which formed a solid state bridge rectifier. The bridge appears to completely bypasses the tube. The tube seems to just stands in the socket doing nothing but glowing. My friend had questioned this before I bought the amp because he says that a single 5AR4 is marginal for four KT88s. Usually you will see two.

I found a site (which I did not realize was in the Phillipines) where I blogged about this. There was some very good discussion there between very knowledgeable electronics guys and they came to a seemingly inescapable conclusion that the tube was there for show - as a marketing add-on to capitalize on the idea that tube rectification is better than solid state.

Here is the link to the thread on that forum (go to page 18)
http://pinoydvd.com/board/index.php?topic=29032.540

We are waiting for Cayin to respond to this issue, but they are in the middle of Chinese New Year (which last 15 days) and are not available for comment. If the evidence weren't so compelling, I would wait for their response before posting this.

There is a slight chance that we missed something in our analysis - but the fact that one of the contributors to the discussion actually pulled the rectifier tube with the amp turned on, and it kept running (now that I think about it, he didn't say how long he left it on, so he may have been running on capacitance) and the fact that a pretty critical analysis of the circuit does not reveal any function for the tube, I decided to post this on Audiogon in order to bring this issue to light in the USA and Europe.
ttbolad

Showing 3 responses by newbee

newbee
4,815 posts
 
"As far as I can tell he wasted good money thinking that the Mullard had some sonic effect."

I disagree regarding whether it was a 'waste of money', at least from his point of view. Perception, often with a bit of gulibility, is the only justification extant for the purchase of many things, especially assessories, but often in the basic components as well. What is the difference between a lot of product puffery, bought hook line and sinker, and a little more graphic deception. Just a different form of Bling perhaps.

Sorry, I couldn't resist.................:-)
newbee
4,815 posts
 
With all due respect to Ttbolad and Captkhz, before we all jump on this band wagon, consider that this consumer alert came to A-Gon via the first post of an unknown person. We've made a lot of charitible assumtions about new posters in the past that proved to actually be from folks who had a hidden agenda

I say that knowing first hand that VAS and at least one of his vendors have no problem stretching the truth about the amplifier output of at least one of thier amps and maintaining the lie in their ad's after they were notified (by me, in writing). As far as I know this was not the doing of Cayin. Some dealers got it right in Europe and a least one in NA.

FWIW.
newbee
4,815 posts
 
LOL re 'blowers', but what I really love is air foils on production cars! Talk about the need for a baby's jock strap! But, given time, we'll probably see that too. :-)
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