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Hey all,

So, it's been almost a year with my 5E3 build completed, and I've been loving every minute of it!!

I finally finished up my cab, and noticed that the chassis was burning hot to the touch after playing for a few hours tonight. I cut holes to vent the tubes in the back panel of the amp, but it seems like heat is building up elsewhere...should I be drilling holes in the back panel to vent out the chassis itself?? Any help would be appreciated! (If it makes any difference, I installed the VVM mod, and was running the amp relatively quietly).

Dan

How much air circulation do you have around the amp? Is it in a combo, head or what?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

It's in a combo cab. There's quite a bit of circulation around the tubes/transformers; however, not so much around the electronics. Perhaps this part should be vented in some fashion as well?

Try it right out of the cab if you can and see how it behaves. Then maybe you can find the real source of the heat.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Will do. I have class tonight...so I won't be able to put it through it's paces until tomorrow

I was running it without the back panel on for quite a while (I was in the process of staining it...and got lazy) and didn't have the heat issue. But I will definitely take your advice and see if I can isolate the source of the heat...will post findings tomorrow.

Dan

Hey Dan...
What speaker did you end up with in your Deluxe, impedance etc.?

Looking forward to some pics of the finished amp when you're done

Joe G

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Some assembly required,
Brain sold separately...

Try an NOS rectifier. I replaced mine and the temp went waaaaaay down.

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Peace,

Paul

That's very interesting. I have to assume the NOS rectifier draws less current than the new ones. Very interesting indeed.

Has anyone done a study on NOS versus new in this regards (current draw?)

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I've never had the chance or thought of testing 5Y3 heater current myself, but it's often been said that Sovtek 5Y3s aren't true 5Y3s. They drop quite a bit less B+ voltage. So I wouldn't be too surprised if they also burn more heater current or have a higher operating temperature.

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Great tones come in small glass jars!

I was always under the impression those Sovteks were just GZ34 rejects...they sure do react differently.


Isn't it the nature of cathode bias to run a bit hotter than fixed bias? Just curious. Cause the tube's are biased higher than the typical 70%...

Many cathode-biased Class AB amps are biased around 90% to 100%. They then use fairly low value cathode cap (eg 50uF or 25uF) to allow the cathode bias voltage to zoom up, and force the bias colder, when the amp's cranking. If you want a stiffer amp with tight bass, you can use a huge cathode cap (1000uF+) and then bias colder, say to around 80%.

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Great tones come in small glass jars!

Where does the 5E3 fall into that bias spectrum?

Going by the 25uF cathode cap value, almost certainly the hot-biased end.

_________________
Great tones come in small glass jars!

I built a Deluxe for a friend last year and used a Trinity combo cab. I also noticed that the chassis does get rather hot, but I assumed that was normal considering you have a bunch of tubes belching out a pile of heat mounted below a slab of metal.

It was never "holy crap I thijnk it's gonna catch fire" hot, but certainly warmer than any other amp I have.

Sitting down now to put the amp through some paces and see what happens, heat-wise. Will report back...and will look into the NOS rectifier tube perhaps as well.

Ended up putting a Vintage30 into the amp (16ohm)...I'm liking how it sounds (dial it in for some crunch, roll back the volume for clean, and life is grand). Just built a small cab out of pine...I'll get some pics up...but prepared to be underwhelmed I'm no woodworker...or much of an electrician! But it works! Now to solve the heat issue...

Stephen, isn't the output of this amp fixed at 8 ohms? What are the implications of a 16 ohm load on the OT?

Joe G

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Some assembly required,
Brain sold separately...

I was always under the impression that running an 8ohm amp into a 16ohm speaker was okay - while running an 8ohm amp into a 4ohm speaker was asking for trouble...PLEASE correct if I'm off base!!!

FWIW, the amp has run flawlessly over the past year (ie no heat problems) without the back panel installed (yes...I"ve literally been putting off finishing this cabinet that long )...I'm wondering if I should vent the chassis to alleviate this issue...

I didn't have a chance to run the amp with AND without the back panel tongiht...so tomorrow's testing will involve removing the back panel and running to see if I still get heat issues. In the meantime, I welcome any other thoughts input - and appreciate all those that have made suggestiosn already.

I'll let the experts speak to the impedance matching.

As for the heat not being an issue with the back panel off, makes sense to me. With the panel installed heat will get trapped inside the chassis. I expect that would be a concern with ANY combo amp with the chassis mounted this way, or upside down. It's something I had never really thought about before, but most of my amps/builds are Marshall-style heads.

The reflected impedance will go up. So the load line will shift.

Plate current will drop, screen current will increase, distortion will increase.

I dont think it will produce any extra heat, but you could try an 8 ohm speaker & see.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

There actually isn't a real hard and fast rule like that with tube amps. It really depends a lot on the construction of the OT. It's important first of all to note that very high flyback voltages get generated across a tube amp OT's primary, which are normally quite a bit higher than the B+ voltage. If you run a higher impedance speaker than a given tap is meant to take, the flyback voltage goes even higher and possible as high as twice B+. If the insulation in the OT has sufficient enough of a voltage rating, the OT will take it. There will also be a reduction in current through the OT. Conversely, if you run a lower impedance speaker on a given output tap than it's supposed to handle, the flyback voltage will decrease, but there will be a corresponding increase in current through the OT. Provided the wire in the windings is rated to handle that level of current everything will be OK.

The bottom line is that if your OT is sufficiently robust you can usually mismatch reasonably safely in either direction. Typically the OTs in most Marshall and Fender amps are built to a tight budget and have little or no slack for increases in current or voltage. That's why you will often come across stories of these amps blowing up after being used with a mismatched speaker load. The RS 18W transformer set used in the original Marshall 18Ws is an exception. Those are extremely robust and can handle some extra current or voltage. The Heyboer-built OTs used in most Trinity amps are also very tough and should in theory have no problems with small mismatches. The one exception is the Deluxe's OT, as it has to be built fairly close to the original Fender OT so that it sounds like a 5E3 Tweed Deluxe should. Being built by Heyboer it will be tougher and better quality than the original stock OT, but I still wouldn't want to risk it, especially with a 4 ohm speaker on the 8 ohm tap. IIRC Fender's Tweed OTs don't have any leeway in terms of current.

HTH

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Great tones come in small glass jars!