JTM45 bright cap question

pb23r · Post by **pb23r** » Fri Feb 03, 2006 9:04 pm

That will be a project for a Saturday afternoon. Like tomorrow! Friday night is more of a cold beer thing...

pb23r · Post by **pb23r** » Fri Feb 03, 2006 10:32 pm

Tried it both ways...overall, i prefer the amp with the bright cap. Without the cap, was just a little too muffled. Keeping in mind that i have no idea what i am talking about, is there another value i can try? What happens if the 500p is swapped for 220p as in the reissue? This is a CeriaTone '45 which has this 100p bright cap and the 500p cap on the board, as described in a previous post.

By the way, that was the very first time i have *ever* taken a soldering iron to my amp.

I think this amp could sound a little better...

Flames1950 · Post by **Flames1950** » Fri Feb 03, 2006 11:44 pm

You can swap the cap for a smaller value if you wish.....the smaller value will raise the frequency "shelf" where the high frequencies will pass around the resistor. I don't have any figures for what the actual frequencies are on hand, mind you..........we'd all have to go back to George's "RC time constants" sticky thread and figure it up........

Flames1950 · Post by **Flames1950** » Fri Feb 03, 2006 11:46 pm

pb23r wrote:As simple as 2 snips with the cutters?

Ouch....any guy with his nuts intact is now cringing, with a chill going up their spine.....

Guest · Post by **Guest** » Sat Feb 04, 2006 11:48 pm

so, is there a lower value than 100 pf that can be used? Is 50pf 'lower' or 200pf 'lower'.?

BashCoder · Post by **BashCoder** » Sun Feb 05, 2006 6:29 am

pb23r wrote: By the way, that was the very first time i have *ever* taken a soldering iron to my amp.

I think this amp could sound a little better...

You know, I picked up a Soldano preamp cheap at a swap meet, and it sounded lame. The first thing I did was to replace the tubes and snip the bright cap off the volume pot of the clean channel. Now I'm in the process of replacing most of the components on that thing. The more I tweak, the better it gets.

Flames1950 · Post by **Flames1950** » Sun Feb 05, 2006 7:28 am

Anonymous wrote:so, is there a lower value than 100 pf that can be used? Is 50pf 'lower' or 200pf 'lower'.?

Depends on what you mean by "lower"........the bigger the number in pF, the lower the frequency that will pass through the cap unhindered. So a 50pF bright cap will let very high frequencies only pass, a 200pF will let somewhat lower frequencies pass through.
Tweed Fenders often had a 47pF bright cap on the volume control, never seen one smaller than that though......

pb23r · Post by **pb23r** » Sun Feb 05, 2006 8:58 am

After messing with the amp (well...my tech did the messing), we concluded that the amp could use a serious upgrade in power tubes and probably a different transformer. I'll be sure to post results.

We are also starting a very early 67 era 100 watt build (the one with 7 caps on the cap board). Although the work will mostly be done by my tech, it should be quite the learning experience for me.

Property values in my neighbourhood are about to fall...

ChrisGS · Post by **ChrisGS** » Tue Feb 14, 2006 9:00 am

Hi ,
You can put a resistor in series with a brite cap or any bypass cap to lessen the effect of that cap .

I'm not sure what value resistor would be good in series with a bright cap ,

But I used a 22k in series with a .68 cathode bypass on the first stage , and it worked out nice .

Chris .