Reducing an Amp's Heater AC Voltage Supply

DonP said:
Combos played very loudly can suffer more than usually. The combination of high temperature and powerful vibration can shorten a heater's lifetime quite badly. It's worth introducing some kind of vibration absorption somewhere between speaker and valve.
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Like dampening rings and preamp tube heat shields?
 
bea said:
It is not a per side. It is 6.3 V. The ECCs have two filaments specified as 6.3V/150mA which are put in series and have a central tap. Thus thei can be run with 12.6V/150mA or 6.3V/300mA.
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Thank you. I'm pretty sure that you have explained this correctly. This is the difference between someone who has proper knowledge of these things and someone who takes the Caveman approach. I'm definitely not proficient... :p

bea said:
I am also a bit surprised that You were using such large resistors: 0.6V*300mA=0.18W. Which means that You could safely use a pair of cheap metal film resistors of 1.2 Ohms/0.6W. Per Tube, of course. Power tube filaments need more, but You can alsways use a couple of smaller resistors in parallel which are readily available.
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This is how I calculated resistance value for each resistor:
AC Heater supply measured 6.8v.
I wanted to drop .5v
Heater current draw:
12AX7's draw 300mA each
6550's draw 1.6A each
3x 12AX7s and 2x 6550s draw a total of 4.1A
4.1 (total current draw) divided by .5 (desired dropping voltage) equals .12 ohms
.12 ohms gets split up into 2 resistors at .06 ohms each

Safe wattage rating for resistors:
4.1 (tcd) times .5 (ddv) equals 2.05 watts
Double the watts for safety = 4.1 watts (I'm using 5 watt resistors)
 
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Robert Herndon said:
Hey, Don...power tubes would stop lighting up, rather frequently. I couldn't get more than 30-45 days out of power tubes, but I was also playing in a house band 6 days a week.
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I didn't notice this post earlier!

Anyways... Where you driving the 100 watt amp hard? Really super loud?
 
syscokid said:
I didn't notice this post earlier!

Anyways... Where you driving the 100 watt amp hard? Really super loud?
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I had a JTM-30 combo for years (1979 to around 1987) and it was constantly overheating. We put two small fans inside it which helped a lot, but it was really hard to trust those old Marshalls.
 
I've been looking at DC buck circuits with an idea of running the heaters off DC instead of AC. It will reduce the hum, and DC voltage regulation is really simple - you could hold the volts within a few millivolts of 6.3 over any range of mains voltages. There are PCBs on ebay that can supply 5 amps, and have a pot to let you set the voltage where you want it.

DC Buck Step Down Converter DC 5A Regulator Voltage Current Adjustable K6 | eBay

Just add a diode rectifier and an electrolytic cap and you are good to go.
 
Robert Herndon said:
I had a JTM-30 combo for years (1979 to around 1987) and it was constantly overheating. We put two small fans inside it which helped a lot, but it was really hard to trust those old Marshalls.
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Those JTM30s sure built-up a reputation for being highly unreliable. But the JCM800s were always pretty solid.
 
JTM 30 is a new one for me never seen one in real life. I sold my JTM-45 collection due to the GEC KT-66 getting rare.

When Russia started manufacturing KT-66 pure trash failed @ 50% during burn in.

My best sounding guitar amp uses a pair of GEC KT-77 and I have a matched quad for back up.

EL34 Mid Plate Skyliner 50 Watt 002.JPG
 
I love these amp geek threads and awesome amp pics just make it more ,well MORE!
And, chicks dig Big IRON!
No wimpy Cut corners ChiCom crap on that OT.

I wouldnt sweat filament voltage off a hair but its good to get into the weeds just so you know how they are a'growin.
 
I have 2 Burman amps brought over from Europe. Both use GEC KT77 tubes. their pretty good to say the least. WE asked KEN Fisher what was the best sounding amp he's ever worked on that no one knows about, he's always said Burman! So, being an incurable Ampaholic I had to locate two. One in Frankfurt, Germany and the other in Glasgow, Scotland. Sounds all their own. Pics soon ….. Oh, and there both ball busters to lift being much heavier than Fender Twins w/ JBL's!
 
Vox AC30 said:
I have 2 Burman amps brought over from Europe. Both use KT77 tubes. their pretty good to say the least. WE asked KEN Fisher what was the best sounding amp he's ever worked on that no one knows about, he's always said Burman! So, being an incurable Ampaholic I had to locate two. One in Frankfurt, Germany and the other in Glasgow, Scotland. Sounds all their own. Pics soon ….. Oh, and there both ball busters to lift being much heavier than Fender Twins w/ JBL's!
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You should know better...

… :pics3:
 
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