Any part that dissipates power, capacitors for example theoretically don't, must be derated for elevated temp. I'm quite sure that if the boards are getting scorched with 1.2W on a 5W resistor the ambient inside the chassis is going way up.
Just noticed that the wooden back forms one side of the chassis, I'm going to try washers between the board and case to leave a 1/16" gap for airflow into and out of the chassis, 1/8" would be even better.
It really makes you wonder about this particular problem. I have the 330 ohm resistors and they barely get hot. My amp was made in Nov. of 1997, so 18 years old and I can touch them for as long as I want not having to pull my finger off because it's too hot. But there are many posts about this very problem and Enzo fixes these all the time. It makes you wonder about the inconsistencies. Here's a question, does the current draw on these resistors increase when the effects loop(aka preamp out, power amp in) is being used? Does it increase when more pedals are used vs. less? And same for the reverb, does the power draw on this supply increase with more reverb dialed in? I'm only just getting started on understanding op amps and SS circuitry, so this seems logical to answering the question. I wonder if they get hotter for the guys who use these features more than those that don't since the TL 072s provide send and return for both features.
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The current through those resistors ought to be pretty steady. A lot of it is simply to keep the zeners flowing. The op amps will not change their current draw much during operation. Whether you use the preamp out signal, it is being produced nonetheless, the op amp doesn't know what you do with the output. Even the reverb driver is always running, turning off the reverb doesn't stop to drive circuit from pushing the reverb pan drive transducer. So again using the reverb or not will not affect the current draw on the power supply.
I'd guess that they made a revision to the transformer to lower the raw feed voltage, or else that they run much hotter when something else goes wrong, or that the entire chassis runs much hotter when something else goes wrong.
So perhaps there is no need for a gap to get some airflow inside the chassis, couldn't hurt.
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This was answered but just to confirm here is another statement that JAN 6L6WGB Sylvania's have GC guts:
http://www.diyaudio.com/forums/tubes-valves/102802-6bg6-6l6gc-top-cap-cheap.html#post1222770
I bought a pair of strong used JAN 6L6WGB's from the mid 1960s so we are going to find out.
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It is fixed and I noted that the original Groove Tubes 6L6GCs bias up at max to 100mA total, whereas the 1960's JANs 6L6GB (actually GC construction) bias up at max to 145 mA total. I think they are just better tubes in better condition.
The internals of the JAN tubes do look large and just like the GCs.
The internals of the JAN tubes do look large and just like the GCs.
Just so you know, the 145 mA bias exceeds the total rating of the tube. The math: .145/2=72.5mA per tube. .0725 X 485v=35.2 watts per tube. They are 30 watt tubes(maybe). I hope you only did this for experimenting and backed off to around 75% max or so. This is 22.5 watts per tube. I guess I should verify that you do have 485 plate volts, but I should still be close.
If you look at the math, I divided 145mA by two to get the value of one tube, using 72.5 mA for each. .0725 X 485=35.16 watts for each. I suppose I could go .145 X 485=70.3 for two. The result is the same. Did I have an error in how I calculated the bias? If so, please point me in the right direction. I understand that screen current can be ignored for bias purposes, is that correct? I am assuming 485 plate volts as per the schematic. Yes, you are correct, TP 30 is for both tubes.
Sorry being so late here, yes I brought up the bias just to push them a bit, then backed it back down.
The amp is fixed but my son moved right around the time I finished it, away from the band that he was in and is so busy with school and work that he has not really used the amp hard. He says it sounds great, perfect.
I concluded that the jumper wire was a factory ECO so I didn't change anything. I didn't recap anything since it is not that old and I'll save that for another time. I did have a lot of ideas to try for mods but he was not using it much so I didn't see it worth doing without him to test them. I just did the repair and reflowed many of the solder joints, and put in some better tubes.
Thanks everyone for all the help!
The amp is fixed but my son moved right around the time I finished it, away from the band that he was in and is so busy with school and work that he has not really used the amp hard. He says it sounds great, perfect.
I concluded that the jumper wire was a factory ECO so I didn't change anything. I didn't recap anything since it is not that old and I'll save that for another time. I did have a lot of ideas to try for mods but he was not using it much so I didn't see it worth doing without him to test them. I just did the repair and reflowed many of the solder joints, and put in some better tubes.
Thanks everyone for all the help!
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I'm hearing this from many people including my son, so I'm wondering what amp is known
for the best overdrive built in without the need for a pedal?
Marshall
Soldano
Orange
????
Again, just my opinion, but while we say the HR amps sound good clean and go well with distortion pedals, that neatly overlooks that there are a thousand different such pedals to use, players' choice. When we start asking what is the "best" amp in terms of internal overdrive, it is like asking which is the best pedal to use with the HR Clean.
And I can get a slew of pedals for my HR without spending a ton. But the overdriving amp you like may be a one-trick pony and sonow what, three more amps?
But even a fair answer relies on taste, just because I may like the Marshall doesn't mean you will.
And I can get a slew of pedals for my HR without spending a ton. But the overdriving amp you like may be a one-trick pony and sonow what, three more amps?
But even a fair answer relies on taste, just because I may like the Marshall doesn't mean you will.