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Post subject: Re: Wanna build an amp kit
Posted: Sat Oct 25, 2014 1:45 pm
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Aspiring Musician
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Nice cab, did you spec it with no handle?

How are you finding the amp overall?


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Post subject: Re: Wanna build an amp kit
Posted: Sat Oct 25, 2014 8:50 pm
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I still need to finish the cab. It is going to be a light natural stain with polyurethane for some protection. I have a fender dogbone handle that I'll put on it once the finish is done. Finishing the baffle now.

The amp sounds great. I love it with the Eminence Maverick speaker. Pleased.


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Post subject: Re: Wanna build an amp kit
Posted: Sun Oct 26, 2014 8:33 pm
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For the record, should anyone find this record of incompetent amp building, I went with minwax "natural" stain and wipe on gloss poly. It appears to match the tung oil tests and should actually provide some protection. Going with black corners.

Pine is soft. This will eventually end up covered in tolex. If I had to do it again I would definitely buy the cabinet from the full kit. For now it is looking rather golden in color.


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Post subject: Re: Wanna build an amp kit
Posted: Thu Nov 20, 2014 2:16 pm
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Soo... How warm should this thing get?

I had it on for a couple three hours last night and it was hot to the touch. Not sure if this is normal for the amp, if I've put something together wrong or if the case isn't providing any air flow.

I was jumpered from bright 2 to normal 1 for most of that time. And running 5751's in place of the 12ax7s.

First time I've noticed it getting particularly warm but then I normally turn it to standby for a while before shutting it off. No sound changes that I can tell. Just warm.


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Post subject: Re: Wanna build an amp kit
Posted: Thu Nov 20, 2014 2:54 pm
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Congrats on the project. Looks great. Please post clips when you get them.

I wonder if you could pop a vent in there. Kind of uglies it up a bit though.

Image


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Post subject: Re: Wanna build an amp kit
Posted: Thu Nov 20, 2014 3:32 pm
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DarkPenguin wrote:
Soo... How warm should this thing get?

I had it on for a couple three hours last night and it was hot to the touch. Not sure if this is normal for the amp, if I've put something together wrong or if the case isn't providing any air flow.

I was jumpered from bright 2 to normal 1 for most of that time. And running 5751's in place of the 12ax7s.

First time I've noticed it getting particularly warm but then I normally turn it to standby for a while before shutting it off. No sound changes that I can tell. Just warm.



Firstly they do run hot, so that in itself is not unusual, question is if it's running too hot.
A couple of suggestions, are you running a GZ34 Rectifier? If so I bet your amp is running high voltages and the 6V6 tubes are way over 100% dissipation (14W for JJ 6V6), JJ's will take it but they will be cooking. Have you checked the idle dissipation of the tubes? It is an exercise well worth doing just so you have an idea of what your tubes may be going through. I actually swapped the GZ34 out and replaced it with a 5Y3, which is more typically the Rectifier used in a Tweed Deluxe. That will drop your voltages down a reasonable amount, but you can also drop more using Zener Diodes in series with the OT Centre Tap (Red/Yellow) to ground wire, with the Cathodes pointing to ground, two or maybe 3 15Volt 5W Zeners will drop about 45 Volts.

That will cool things off a bit and your tubes will last longer.

A small personal fan directed into the back of the amp will also create some air movement and reduce temps noticeably.

Also if using the GZ34 Rectifier, you don't need to use the Standby at all when turning on/off, in fact it's easier on the tubes if you don't.

Here's how to check the dissipation, these numbers are from my amp, just plug in the numbers you measure on your amp (for the screen current just use 3.5ma, it'll be close enough):

I measured following to start with:
Voltage across Cathode Resistor = 21 volts
Actual Measured Resistance of Cathode Resistor = 250 Ohms
Plate Voltage (Pin3 to Ground) = 357 volts

Plate Current calculations:
Cathode Resistor Voltage (21 volts) / Cathode Resistor Ohms (250) = 0.084 (84 milliamps)
This is the Cathode Current (including screen current) for BOTH Tubes.
Subtract the screen current (measured to be 3.5ma) = 80.5ma
Divided by 2 (tubes) = 40.25ma Plate Current per tube

Idle Dissipation calculations:
Plate Voltage (357 volts) - Cathode Resistor Voltage (21 volts) = 336 volts
multiplied by Plate Current (.04025ma) = 13.5 watts


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Post subject: Re: Wanna build an amp kit
Posted: Thu Nov 20, 2014 9:21 pm
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No457 Snowy wrote:
...if using the GZ34 Rectifier, you don't need to use the Standby at all when turning on/off, in fact it's easier on the tubes if you don't...


Curious as to your thinking on this. Conventional wisdom says that you use a standby switch to let the output tubes warm up first before applying high voltage, especially with higher wattage amps. Sure, any rectifier tube brings the high voltage up slowly after a small delay, but IMO this isn't really enough time to let the tubes warm up first, with any rectifier tube, GZ or other.

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Post subject: Re: Wanna build an amp kit
Posted: Fri Nov 21, 2014 1:00 am
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Shimmi we risk derailing the thread on that one, the Internet is littered with long threads on that one topic, heaven knows I've been involved in some, but not again. :wink:


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Post subject: Re: Wanna build an amp kit
Posted: Fri Nov 21, 2014 9:33 am
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Ran it for about an hour last night with out the bright 2 to normal 1 jumper and it was way cooler. Finally found my meter (It was in the garage where I built the amp. Go figure.) so I'll get some numbers this weekend.

Thanks for the help!

BTW, what would be a kinder rectifier tube for such an amp?


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Post subject: Re: Wanna build an amp kit
Posted: Fri Nov 21, 2014 10:11 am
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DarkPenguin wrote:
Ran it for about an hour last night with out the bright 2 to normal 1 jumper and it was way cooler. Finally found my meter (It was in the garage where I built the amp. Go figure.) so I'll get some numbers this weekend.

Thanks for the help!

BTW, what would be a kinder rectifier tube for such an amp?


Pick up a NOS 5Y3, they are not expensive, I have an old RCA brand in mine. JJ also make a 5Y3 that runs correct voltage (similar voltage to the NOS tubes). Steer clear of the Sovtec 5Y3 though, it runs higher voltages than NOS, or JJ.


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Post subject: Re: Wanna build an amp kit
Posted: Sat Nov 22, 2014 11:13 am
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I jump channels but don't find heat to be an issue. Something may be out of spec. I run a GZ34. I agree, a 5Y3 rectifier will cool things down a bit if it worries you. So far I've had no issues running it as is and it's going on two years and it's all stock.

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Post subject: Re: Wanna build an amp kit
Posted: Sat Nov 22, 2014 1:43 pm
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That's very true Supro, the first one I built still has the GZ34 in it, I sold that amp to a fellow I regularly jam with and he runs it hard and often, it's now his only amp so it is in constant use out and at home, unbelievably it still has the original tubes in it, the ones that came with the kit. it's like 3+ years old now and he has hammered it hard, It always gets cranked and he hits it pretty hard with a Les Paul, very nice creamy tones, when we jam we do so in an old factory so we have free reign as far as volume goes. :lol: He loves it and only commented recently how the tubes still sounded so gutsy and strong, it really is testament to those JJ 6V6's and also to a bullet proof little amp.

I really only changed my other Deluxe to a 5Y3 to see what the differences were heat wise, as well as sonically and to take measurements etc, it's a good learning exercise too. It'll definitely help if he is concerned about the heat and if he puts other branded 6V6's in with the GZ34 they might be toast a LOT faster than the JJ's.


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Post subject: Re: Wanna build an amp kit
Posted: Sat Nov 22, 2014 5:55 pm
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I agree Snowy, JJ's 6V6 are about the only current production tubes I'll run. Never had a problem with them in any of my amps. Very tough tubes. I crank the snot out of that amp and push it with P90's.

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