Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: macula56 on March 28, 2011, 06:48:49 pm

Title: KT66 placement.
Post by: macula56 on March 28, 2011, 06:48:49 pm

Are there any real guidelines about placement when building an amp with KT66's? do they need to be further from the PT and OT than 6L6's? and how about the space between them? and help greatly appreciated. JMac.

Title: Re: KT66 placement.
Post by: RicharD on March 28, 2011, 06:54:45 pm

Rule of thumb, keep at least 1 tube width spacing around each tube.  Big tube, big tube space, little tube, little tube space.  The higher the gain, the more you wanna spread things apart.

Title: Re: KT66 placement.
Post by: macula56 on March 28, 2011, 07:05:17 pm

i have seen people using them in Fender's and they are pretty close.

Title: Re: KT66 placement.
Post by: RicharD on March 28, 2011, 07:12:55 pm

Some folks like to pack it in there.  Personally, I believe if you have the space you should use it.  Easier to service, bla bla bla.

Title: Re: KT66 placement.
Post by: andrew_k on March 28, 2011, 07:21:53 pm

From GEC's KT66 datasheet:

"A pair of valves working at maximum ratings should be mounted at no less than 9cm (3.5in) between centres"

Reference: http://www.hifitubes.nl/weblog/wp-content/gec-kt66.pdf - bottom of page 4

Title: Re: KT66 placement.
Post by: macula56 on March 28, 2011, 07:24:08 pm

Marshall JTM45 circa ’64 Clapton version serial # 1002

http://www.vintageamps.com/jtm45Collection/1002/Top1.jpg

Title: Re: KT66 placement.
Post by: shortfuse on March 30, 2011, 12:00:52 am

I built the Hoffman Plexi 50 and used KT88's.  I used a JTM45 chassis which was smaller 17.5 inches wide and had some choices I had to make to get all 3 caps the 2 power tubes and 3 12AX7's across the back of the chassis.  So my tubes are about 1 inch apart glass to glass and I have had no issues to speak of.  I use this amp several time a week also.
But give the choice again I would go with the larger chassis and space thing a bit further apart.

Title: Re: KT66 placement.
Post by: andrew_k on March 30, 2011, 09:02:49 pm

macula56: You started the thread asking if there are guidelines. Indeed there are, as provided above.
If you instead mean "what can I get away with", forum member Darryl has a 6xKT88 amp running at just shy of 800V (is that still the case Darryl?) where the bottles are actually touching. I've stood in the same room as this thing at full power on two occasions now. Not for the faint of heart or those fond of their hearing, but entirely possible.

Title: Re: KT66 placement.
Post by: macula56 on March 31, 2011, 02:04:58 pm

that sounds interesting andrew_k. i just wanted some general stuff. everything so far makes sense to me. i am not going to cram everything all together so that it all touches, but i do have limited space. thanks to everyone for the excellent replies. JMac