Radford STA15 Restoration.

[Marchbanks]

Hey Marchbanks, you are correct of course. That shelf gets quite toasty indeed, mainly above the mains transformer, but no scorch marks yet after a week of evenings like this.. keeping an eye though! This shelf spacing was designed for Stereo 20.

It’s not so much the possible damage to the shelf that would concern me, more the likelihood of trapping warm air in and reflecting heat into the amp causing the internal temperature to rise. I rang Will at RR a while back and (off the top of his head, I wouldn’t hold him to it) he suggested that on an open shelf like yours and mine 10cm clearance would be just about sufficient.

 

[Tony L]

Valve power amp: always top shelf and unimpeded airflow as far as I’m concerned, though it has to be pointed out back in the 50s and 60s they were regularly contained in ‘radiogram’ style cabinets with next to no airflow. I suspect this caused many of the problems with transformer wax leaking from Leaks, Quad IIs etc, caps drying out and failing etc. Some of the commercial cabinet designs I’ve seen (in Imhofs catalogs, old copies of Gramophone etc) were just hopeless from an air-flow perspective. Basically none.

 

[Chops54]

At 30kgs apiece my 211s go on the bottom shelf

On a lighter note I missed a pair of Radford monos last year. I was undecided on whether I should let the 211s go. I should have bought them and worried about that later

 

[Raoul Duke]

It’s not so much the possible damage to the shelf that would concern me, more the likelihood of trapping warm air in and reflecting heat into the amp causing the internal temperature to rise. I rang Will at RR a while back and (off the top of his head, I wouldn’t hold him to it) he suggested that on an open shelf like yours and mine 10cm clearance would be just about sufficient.

Aah yes I see where you're coming from, I was quite crap at thermodynamics but no doubt the shelf proximity would slow the escaping heat somewhat. I will have to change this up for summer when room temps are 10 - 20 degrees higher!

 

[eguth]

Aah yes I see where you're coming from, I was quite crap at thermodynamics but no doubt the shelf proximity would slow the escaping heat somewhat. I will have to change this up for summer when room temps are 10 - 20 degrees higher!

Would it not be possible to cut some, preferably many, holes in the shelf- say 1 inch diameter holes? If 'fall through' is of concern, you could fasten some metal open mesh to the underside.

I think Marchbank's concern is wise.

My (upgraded) STA25/III valve sockets are gold- plated porcelain. I don't know if this affects temp. One input valve is fitted with 'accordian -style' metal fins. This does help air flow and heat dispersion.

Most of the heat comes from the KT77 output valves. My matched sets (quad matched) of JJ.s perform superbly and last a long while- with no failures- so far.

The other EF86/ Military equivalent input valves have two 'washer like' dampers on each valve. Again I do not know whether this affects temperature- but it does improve fildelity of sound (slightly).