Dennis Had Inspire Amps

[Wgarcia]

My Shuguang 274B arrived yesterday and is not only beautiful to look at (just cool…seriously), it works really well. I've bought some Psvane and other Chinese tubes over the years and have been somewhat disappointed with the fit and finish (some, not all) and have had a couple simply fail…but this 274B seems really well made and, of course, hasn't failed yet (almost a day in service).

[Comzee]

I was moving my kt88 Fire-Bottle when I heard something rattling inside, so I took the back off.

It was a rubber sleeve that wrapped around a resistor near the PSU. The heat literally baked it off, it was hard and rattling in the case.
Resistor pictured: https://c1.staticflickr.com/5/4299/3...662e931d_b.jpg
It's the one that says XICON.

I also noticed while I was looking in there that similar resistors near the back melted the coating off some other resistors, pictured: https://c1.staticflickr.com/5/4297/3...82acbedb_b.jpg
I hand parted those four resistors apart as far as the wire would let me. They were originally smashed together with no space. I also drilled holes on the underneath cover. Three holes under the PSU, and four under those four resistors.
Now when I have it on, I can squeeze my hand underneath the Fire-Bottle and feel 100F+ heat billow out of the amp

I always knew the thing got hot, but I assumed Dennis knew best as far as heat effects. I mean a metal box with no vents is a torture chamber for electrical parts.
I know the holes in the bottom cover might reduce resale, and some might think it ugly, but a steel box with no vents is no bueno in my book. Just thought I'd pass the info along.

[Bombadil]

Inspected mine right away. As I have the 17wpc version, I was concerned that there would be even more heat buildup. Plus I run less efficient speakers and thus probably at higher output wattages. But no sign of any damage in mine. My circuit layout looks different than yours. Does yours have the 20W output transformers? Perhaps those run a bit cooler, as they are larger, than the 15W ones?

[pstrisik]

Originally Posted by Comzee

I was moving my kt88 Fire-Bottle when I heard something rattling inside, so I took the back off.

It was a rubber sleeve that wrapped around a resistor near the PSU. The heat literally baked it off, it was hard and rattling in the case.
Resistor pictured: https://c1.staticflickr.com/5/4299/3...662e931d_b.jpg
It's the one that says XICON.

I also noticed while I was looking in there that similar resistors near the back melted the coating off some other resistors, pictured: https://c1.staticflickr.com/5/4297/3...82acbedb_b.jpg
I hand parted those four resistors apart as far as the wire would let me. They were originally smashed together with no space. I also drilled holes on the underneath cover. Three holes under the PSU, and four under those four resistors.
Now when I have it on, I can squeeze my hand underneath the Fire-Bottle and feel 100F+ heat billow out of the amp

I always knew the thing got hot, but I assumed Dennis knew best as far as heat effects. I mean a metal box with no vents is a torture chamber for electrical parts.
I know the holes in the bottom cover might reduce resale, and some might think it ugly, but a steel box with no vents is no bueno in my book. Just thought I'd pass the info along.

That's concerning! I will check mine and maybe cut a replacement bottom from hardware mesh (home depot/lowe's) to allow ventilation while preserving the original bottom plate even if no evidence of heat damage - just to be safe.

[BearCityUSA]

Originally Posted by Comzee

I was moving my kt88 Fire-Bottle when I heard something rattling inside, so I took the back off.

It was a rubber sleeve that wrapped around a resistor near the PSU. The heat literally baked it off, it was hard and rattling in the case.
Resistor pictured: https://c1.staticflickr.com/5/4299/3...662e931d_b.jpg
It's the one that says XICON.

I also noticed while I was looking in there that similar resistors near the back melted the coating off some other resistors, pictured: https://c1.staticflickr.com/5/4297/3...82acbedb_b.jpg
I hand parted those four resistors apart as far as the wire would let me. They were originally smashed together with no space. I also drilled holes on the underneath cover. Three holes under the PSU, and four under those four resistors.
Now when I have it on, I can squeeze my hand underneath the Fire-Bottle and feel 100F+ heat billow out of the amp

I always knew the thing got hot, but I assumed Dennis knew best as far as heat effects. I mean a metal box with no vents is a torture chamber for electrical parts.
I know the holes in the bottom cover might reduce resale, and some might think it ugly, but a steel box with no vents is no bueno in my book. Just thought I'd pass the info along.

You may remember I cooked a couple resistors with my PSE a while back because I was running tubes (6K6s) which were not compatible with the voltage of the circuit. When inquiring with DH I learned the rubber sleeves on the resistors are for secrecy. Heat shrink to hide the values from copycat eyes. Anyway, I would contact DH about this. If this lack of ventilation was a design flaw others would have had the same issue. I have a feeling something is out of whack. It may have been a tube going nuclear that intern caused a Cap to vary with use and then cause further heat due to varying voltages and to much current draw. I guess what I am saying is that the holes may help with a symptom but not solve the root cause.

[Comzee]

Originally Posted by BearCityUSA

I guess what I am saying is that the holes may help with a symptom but not solve the root cause.

I was using kt66 pair with 6sn7 and 5u4g rectifier, all standard Dennis recommended tubes.

[Bombadil]

And on mine, with no damage, I have been really pushing it. Running KT120 with GZ34 rectifier for maximum output. I do have a bit of a larger chassis than the standard KT88 HO. So more space and components are not as crammed together. I cannot ever remember my chassis feeling hot, or even moderately warm.

[BearCityUSA]

Originally Posted by Comzee

I was using kt66 pair with 6sn7 and 5u4g rectifier, all standard Dennis recommended tubes.

Yep, those are a fine selection of tubes. IMHO though something is a miss besides vent holes causing things to run to hot and burn up passives. My KT amp runs cool cool. Chassis is a touch above room temp and PSs are slightly warm regardless (mid 80's F) of the tube combos. I renew my suggestion to contact DH and get his take.

[Bombadil]

My chassis is 14.25" x 7.5" I've been under the impression that this is a bit larger than the standard. But don't really know.

[pstrisik]

I received this from Dennis to pass on to allay concerns:

The wire wound resistors I am using are 5 watt resistors and I run them between .8 to 2.1 watts. Well within their design range. I use heat shrink to prevent “outsiders” from copying by simply observing the values. Some of the heat shrink I have discovered was a marine version that became brittle and cracked. This in no way effects the part or performance. Most all the parts I use have a heat rating of from 85C to as high as 230C. I guess I’ll simply stop putting the shrink tubing over the resistors as it may cause concern.