We've had a number of customers try to use this tube as a replacement for the 6AS7G. Universally their experience and also IME it is more likely to arc than the 6AS7G. However the 6AS7G has fairly lightweight links from the tube base to the cathode which can blow out, severing the connection to the tube (during the arc, it can be considered to be shorted). With the 7236 the links rarely fail, so the internal short does not stop. So if you use this tube I recommend that you self-bias it and use a fuse to protect other elements in the circuit.
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7236 and 5998/421A worked extremely well as SE driver tubes - the 7236 was a bit cleaner/brighter, while the 5998/421A produced a warmer sound.
All of my 7236s were Sylvanias with the metal base ring. The best 5998s rivaled the 421A, but 5998 exhibited quite a bit of sonic variation.
Overall, I preferred the 421A, but much will depend upon the rest of your system.
I did not try the 6AS7/6080, because I needed some gain
Note: Many pass tubes have notoriously mismatched sections...the 421A consistently exhibited the best section matching.
Jim
Frank is Fdegrove. Lilliput is a Tim de P design incorporating H2 cancellation..
1. Agreed.
2. Because the design uses common values, you had the parts available and were able to knock one up in couple of hours has nothing to do with whether or not the designer attempted a degree of H2 cancellation.
3. I built an 'improved' version of the amp with ccs'd pc86 driver and led bias, and the amount of H2 it produced was horrendous, rendering it pretty well unlistenable. I was able to achieve much more satisfactory results playing around with different driver tube plate resistors and a small pot in each cathode.
4. if you are going to try distortion cancellation it is a good idea play around with input tube operating points USING THE SPEAKERS YOU INTEND TO USE, as the output tube loadline depends on the impedance of the speaker it is driving. To complicate matters, because speaker impedance also varies with frequency, H2 cancellation works best when driving speakers with a fairly flat impedance curve.
5. If I were to build the amp now, I would follow the schematic exactly, and then assess the effects of varying the input tube OP and loadline on distortion. I would definitely not use a ccs and led bias.
6. If the design was changed to incorporate cathode feedback around the output transformer to linearise output tube transfer characteristics to something approximating a good DHT, then a ccs and led on the driver may well produce superior results. This is now my preferred way of building with pass tubes.
This article may shed further light on the matter.
http://www.audioxpress.com/magsdirx/ax/addenda/media/DickerOddsEvRev.pdf
I completely agree with the author's view that it is preferable to design linear amplifying stages that do not require cancellation.
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I believe that neither the Lilliput (6080 driven by 6922) nor the Triodino (5998 driven by 6201) were designed by Tim de Paravicini. The Triodino design first appeared in a Costruire Hi-Fi article of April 1993 by Cristiano Jelasi and Ciro Marzio and the Lilliput design followed some years later in a November 1996 article by Ciro Marzio. I've never seen any reference to de Paravicini related to these designs. I understand there may be some confusion because of the whop names involved but de Paravicini is English, and Jelasi and Marzio are Italian.
John
http://www.thefreedictionary.com/Knee+jerk+reaction
I said I would not use a ccs and led in this instance because the output stage of this amp produces lots of H2, which can be cancelled to some degree by the first stage. Having used a ccs’d PC86 as driver, I am speaking from experience.
I then went on to say
If the design was changed to incorporate cathode feedback around the output transformer to linearise output tube transfer characteristics to something approximating a good DHT, then a ccs and led on the driver may well produce superior results. This is now my preferred way of building with pass tubes.
ie: it is preferable to design linear amplifying stages that do not require cancellation
I can write it in simpler English if you wish.
With any OTL it is a good idea to use some sort of current-limiting resistors with whatever power tubes you use, but I would install them in series with the cathodes, not the plates. They will be far more effective in the cathode circuit.
I have an OTL amp by Atma-sphere which uses 10x 6H13C tubes. While I like the amp, its homey looks are not to my taste. One particular irritant is the Coke-bottle shape of the 6H13Cs. I read somewhere that the 7236 is a direct substitute. Is that true? I tried to get a confirm from the manufacturer -- of the amp -- but had no response.
You would have to contact us directly first
We've not heard from you.To answer the question: DO NOT use this tube! Although it will run in the amplifier, it tends to develop hard shorts that can damage a loudspeaker.
OTOH if you use 6080s: if NOS let them run in Standby with no B+ for a minimum of 72 hours. Grid heatsinks can be an issue on 6080s (this is why we use the 6AS7G as it has large grid heatsinks). If you have smaller heatsinks in the tube the grid can overheat and warp. This leads to arcing- a common problem with 6080s. But not all of them do it. You have to regard the use of 6080s as experimental.
OK, thanks for the message. I bought 10x 6080s, I will try them the way you suggested and report ack. BTW, below is the message I sent you, may be kt got stuck in a junk filter?:
From: Ali Elam <aelam@nyc.rr.com>
Date: June 20, 2012 8:21:02 PM EDT
To: "ralph@atma-sphere.com" <ralph@atma-sphere.com>
Subject: S30MkIII
Hi Ralph,
I bought one of these from you a number of years ago and have been using it happily.
Question: Can 7236 tubes be used with this amplifier rather than the original 6H13C it came with? I am just a little tired of the Coke bottle look! Alternatively are there other straight-side tubes *I can use?
All the best,
Ali Elam
NYC
From: Ali Elam <aelam@nyc.rr.com>
Date: June 20, 2012 8:21:02 PM EDT
To: "ralph@atma-sphere.com" <ralph@atma-sphere.com>
Subject: S30MkIII
Hi Ralph,
I bought one of these from you a number of years ago and have been using it happily.
Question: Can 7236 tubes be used with this amplifier rather than the original 6H13C it came with? I am just a little tired of the Coke bottle look! Alternatively are there other straight-side tubes *I can use?
All the best,
Ali Elam
NYC
Unfortunately my experience is that the 6H13C is the best sounding version of the 6080. I have tried RCA and Mullard and both have a strident top end in my amplifier. I keep trying the other 6080 and the result is always consistently the same - 6H13C is smoother at the top and punchier in the bottom end.
Shoog
Shoog
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