YAOB (yet another one-zero-two build)

martin manning · Post by **martin manning** » Fri Jul 27, 2012 8:14 pm

You could get by with a 5A, the mains fuse in the amp is a 5A, albeit a slow-blow. Usually you'd bring the voltage up slowly too. That said if you're buying one, I think a 10A would be better.

talbany · Post by **talbany** » Fri Jul 27, 2012 8:39 pm

3 amp Slo-Blo is what Dumble rated

T

martin manning · Post by **martin manning** » Fri Jul 27, 2012 9:04 pm

I see you are right Tony. So how did the CE chassis get marked 5A, I wonder?

And, rated power on the Twin Reverb PT only rolls up to about 1.5A on the primary, so 3A would be a 2x margin (not including start-up surges).

talbany · Post by **talbany** » Fri Jul 27, 2012 9:12 pm

5a is over kill..I think the SVT bass amps are rated 5a
I've run 2a slo on them before but have blown a few at in rush..

Tony

martin manning · Post by **martin manning** » Fri Jul 27, 2012 9:18 pm

I agree based on the PT rating. So how big is your Variac? I like big ones so I can make my vacuum cleaner sound like a turbine...

talbany · Post by **talbany** » Fri Jul 27, 2012 9:34 pm

Yeah that's cool,and looks great on the bench I'll bet.. Mine is just a 5a cheap China..Early on I used the variac a bunch but hardly ever anymore..I think the last time was to form some caps..The new reset fuses are cool..There great if you want to keep a closer tolerance and not have to keep extra fuses.

Tony

Max · Post by **Max** » Sat Jul 28, 2012 5:25 am

talbany wrote:3 amp Slo-Blo is what Dumble rated

martin manning wrote:I see you are right Tony. So how did the CE chassis get marked 5A, I wonder?

If you look at all the pictures here http://www.roblivesey.com/dumble/ you'll see that on original 2nd, 3rd, transition and 4th generation 100W chassis the fuse is specified "3 AMP SLO-BLO" and on original 5th and 6th generation 100W chassis the fuse is specified "5 AMP SLO-BLO".

All the best and a great weekend to all here!

Max

Structo · Post by **Structo** » Sat Jul 28, 2012 2:38 pm

That is weird.

#124 has a 3 Amp fuse and the newer ODS have 5 Amp.

I see that Robben's #102 has a label over the screen printing with a 5 Amp label.

So maybe the 3 Amp was borderline that could blow after a while or depending on the wall voltage.

Max · Post by **Max** » Mon Jul 30, 2012 6:21 am

martin manning wrote:And, rated power on the Twin Reverb PT only rolls up to about 1.5A on the primary, so 3A would be a 2x margin (not including start-up surges).

Structo wrote:I see that Robben's #102 has a label over the screen printing with a 5 Amp label.

IMO the PT on this picture of #0102 seems to be larger than a Twin Reverb PT. And if Tony's layout of #0102 is correct, then the PT in the original #0102 isn't a Fender Twin Reverb PT but a Fender 026554 multi volt PT that AFAIK can be used with line voltages from 100V up to 240V: https://tubeamparchive.com/viewtopic.ph ... 264#140264

Cheers,

Max

aflynt · Post by **aflynt** » Mon Jul 30, 2012 1:25 pm

Max wrote:
martin manning wrote:And, rated power on the Twin Reverb PT only rolls up to about 1.5A on the primary, so 3A would be a 2x margin (not including start-up surges).

Structo wrote:I see that Robben's #102 has a label over the screen printing with a 5 Amp label.
IMO the PT on this picture of #0102 seems to be larger than a Twin Reverb PT. And if Tony's layout of #0102 is correct, then the PT in the original #0102 isn't a Fender Twin Reverb PT but a Fender 026554 multi volt PT that AFAIK can be used with line voltages from 100V up to 240V: https://tubeamparchive.com/viewtopic.ph ... 264#140264

Cheers,

Max

I think Martin was referring to my amp which does have a Twin Reverb PT there. Either way I'm guessing a 5 amp Variac would work fine. I'm going to ask around and see if there's anyone locally that I can borrow one from to measure the voltages in the amp with 120VAC coming in.

Thanks again for all the help!
-Aaron

martin manning · Post by **martin manning** » Mon Jul 30, 2012 1:34 pm

You can adjust your measured voltages by the ratio of 120/actual line voltage and get pretty close.

aflynt · Post by **aflynt** » Mon Jul 30, 2012 1:54 pm

martin manning wrote:You can adjust your measured voltages by the ratio of 120/actual line voltage and get pretty close.

Okay. So given my previous three measurements (428VCD B+ @ 118VAC Line, 414VCD B+ @ 116VAC Line, and 424VCD B+ @ 116VAC Line) the B+ at 120VAC Line with this PT would be somewhere between 428VDC and 438VDC. Since according to talbany these PTs (Twin) are usually dead on 450VDC, I think I will wire that Showman PT in there tonight and see how things go.

-Aaron

Structo · Post by **Structo** » Mon Jul 30, 2012 2:07 pm

My Magnetic Components Twin Reverb PT has a plate voltage of 436v biased at 31ma with a wall voltage of 119.2vac

There are a few factors that will change the plate voltage.

I think if you are in the 430-450 range you are fine.

aflynt · Post by **aflynt** » Mon Jul 30, 2012 2:14 pm

Structo wrote:My Magnetic Components Twin Reverb PT has a plate voltage of 436v biased at 31ma with a wall voltage of 119.2vac

There are a few factors that will change the plate voltage.

I think if you are in the 430-450 range you are fine.

Hmm... Maybe I just have it biased too hot. I've been running it around 41ma figuring that's about 60% of max assuming 30W tubes. Do you guys usually bias the Winged C's for 60% assuming 23W or 30W max?

-Aaron

boldaslove6789 · Post by **boldaslove6789** » Mon Jul 30, 2012 5:26 pm

aflynt wrote:
Structo wrote:My Magnetic Components Twin Reverb PT has a plate voltage of 436v biased at 31ma with a wall voltage of 119.2vac

There are a few factors that will change the plate voltage.

I think if you are in the 430-450 range you are fine.
Hmm... Maybe I just have it biased too hot. I've been running it around 41ma figuring that's about 60% of max assuming 30W tubes. Do you guys usually bias the Winged C's for 60% assuming 23W or 30W max?

-Aaron

Might want to Bias @ around 32mA, 41 seems kinda high.

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