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Hello all,
I have built my first tweed trinity kit. It sounds great, looks good as well. I stuck the chassis in a blues jr cab. I think it is running a little hot though. I have two rectifier tubes. The sovtek that came with the kit and a NOS 5y3WGT.



I will post some more pictures later. I would like to get some idea about the voltages first as the chassis does get quite hot with the sovtek. It gets hot with the NOS tube as well just takes much longer. You can touch it just fine but it is hot.

Is this normal?

Below are the voltages.

with the sovtek the voltages are as follows:
B+ on standby 363
B+ no standby 415
V1 148 pin1, 2.3 pin3, 138 pin6, 2.3 pin8
V2 176 pin1, 1.34 pin3, 218.8 pin6, 17.5 pin7, 48.3 pin8
V3 406 pin3, 364.4 pin4, 22.75 pin8
V4 407 pin3, 363.7 pin4, 22.7 pin8

with the NOS tube
B+ on standby 365
B+ no standby 378
V1 131.4 pin1, 2.13 pin3, 126.2 pin6, 2.13 pin8
V2 159.4 pin1, 1.23 pin3, 198.4 pin6, missed this one(just noticed) pin7, 44.5 pin8
V3 371.5 pin3, 334 pin4, 20.5 pin8
V4 372 pin3, 333 pin4, 20.5 pin8


A big thank you to Stephen for being so helpful with the order.

Tube amps do run hot but if the chassis is getting to warm to hold your hand on then you've got an issue.

It looks like there isn't much ventilation in the back of the cab. Take a look of other cabs (Tweed in particular) and you'll see there is a bit more room for airflow. Cutting some oval ports in the back wouldn't be a bad.

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I did just that. The picture doesn't reflect the latest "mod" to the cab. I have a pretty large ventilation hole now. It is still warm.

I have had other tube amps from Fender and they all run cooler. I have a friend who has part owner of a small amp company that shall remain nameless. They made a deluxe clone. He did say they ran cool. He was more of a player than technical, but he would know cool vs hot.

Is there anything further I can check? Everything runs fine, sounds fine, works fine. Just a little hotter than I expected. Could be normal. This isn't my first build of a tube amp. The other amp runs great, sounds good, is much cooler. It is a head kit.

thanks,
Steve

I believe I measured the voltage drop across the cathode resistor as 20V. Doesn't seem like enough.

viewtopic.php?f=12&t=3173

Follow this.

See if your output tubes are running too hot.

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http://pdfelectronics.com

Lots of room for airflow

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http://pdfelectronics.com

Using this calculation I came up with 13.75 watts

Voltage across Cathode Resistor = 20.3 volts
Actual Measured Resistance of Cathode Resistor = 250 Ohms
Plate Voltage (Pin3 to Ground) = 368 volts

the back isn't pretty. I don't have a tweed cab yet but I am gonna play this amp at a small venue.


thanks

Mine runs pretty cool, but I'm dissipating about 12 watts - 13.75 seems a bit high. Maybe you want to try changing the bias resistor.

I think there is a bit too much air restriction. Take the back off and see how hot it gets. Some do run a little hotter than others but of you can keep you Hand on it, it is OK.

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

Indeed, it's running a little hot but not terrible.

Changing the cathode resistor to 270R-280R would probably do the trick.

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http://pdfelectronics.com

All good suggestions. Cod the PT being right on the chassis have an affect? It seems that we removed the 4 nuts on the tranny and mounted the tranny flush.

Thanks everyone

ok, played it for an hour with the back off. Still pretty hot.

Changed out the cathode resistor with a 270 Ohm. Still hot.

The voltages after the change are higher
B+ on standby 363
B+ 380
V1 1-136, 3-2.17, 6-128.2, 8-2.3
V2 1-162.5, 3-1.27, 6-202.6, 7-16.4, 8-45.3
V3 3-373, 4-337, 8-21.4
V4 3-375, 4-338, 8-21.4

21.48 volt drop across the cathode resistor

It is definitely not as hot with the NOS tube.

Still sounds really good though.

If you wanted to you could run a 15 Volt 5 Watt Zener diode between the PT centre tap and ground, that would probably get the B+ down to about 365V or so and drop the dissipation a bit.

Snowy

I have gotten the heat down by making a change to the way I mounted the PT. I had incorrectly mounted the PT flush to the chassis. I put the small nuts back between the chassis and the PT and the temp has gone down significantly. The amp is working great. I have had it out at a couple of shows and it is a champ. Sounds great!
thanks for all the suggestions!
Steve

Good tip to keep in mind. We always leave the buts on and a gap between the chassis. It also provides some hum isolation as well.

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