7236 vs 6AS7 ?

[jlsem]

Originally Posted by mach1

Frank is Fdegrove. Lilliput is a Tim de P design incorporating H2 cancellation..

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

[SemperFi]

Originally Posted by jlsem

... some confusion because of the whop names involved ...
John

[mach1]

Whiplash.

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.

[atmasphere]

Originally Posted by thoriated

Since 'atmasphere' is here, perhaps he can refresh my mind as to the value of adding a low value resistor (in series with the plate?) in helping with 6as7g longevity in an OTL application?

Thanks in advance.

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.

[toptip]

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.

[flatheadmurre]

I think Atmasphere stated earlier in the thread that it´s more likely to get arcing in 7236 then 6AS7G perhaps a reason to avoid it.

The slimmed version of 6AS7G is 6080.

[toptip]

Thank you, very kind. They are a quarter the price too!

[atmasphere]

Originally Posted by toptip

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.

[toptip]

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

[Shoog]

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