Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: blues man on March 11, 2011, 08:12:55 pm

Title: modifed 5e5
Post by: blues man on March 11, 2011, 08:12:55 pm

I have just modified my 5e5 and added a master vol pre phase inverter and an xtra stage of gain. The sustain and tone are incredible. At least from the amps I've built so far. You get a real nice disortion at a low vol and if you crank the master up you can roll back the vol on your guitar and get a clean tone and control the distortion with your guitar. I have posted the schematic.

Title: Re: modifed 5e5
Post by: Willabe on March 11, 2011, 08:46:21 pm

Got any pics for us?


               Brad         :icon_biggrin:           

Title: Re: modifed 5e5
Post by: blues man on March 11, 2011, 08:57:38 pm

I have to snap some pics. I only have the originals from when I first built the amp which was a 5e3. This amp has gone from a 5e3 to a 5e5 to what it is now. I cant afford to keep building new amps to find out what they sound like so I started rebuilding them. I try to post some pics tomorrow. This one is a keeper.

Title: Re: modifed 5e5
Post by: tubenit on March 12, 2011, 05:57:47 am

Nice!!  Thank you for sharing the schematic!

You are sort of heading the Trainwreck direction ala tweed style. You could call that the "Double T"
 :l2:

Glad you are enjoying the amp.

With respect, Tubenit

Title: Re: modifed 5e5
Post by: LooseChange on March 12, 2011, 06:36:06 am

Nice, I like that.

Title: Re: modifed 5e5
Post by: blues man on March 12, 2011, 06:55:23 am

Thanks for the compliment. I searched the net trying to find a master vol pre split phase inverter sch. but could not find one so I designed one myself. I blew a brand new rca 5u4 because I didn't have a cap after the third stage right before the master. The amp was really loud and blew when I turned it off. The output transformer is a bogen designed for 7868 tubes that I have used for 6v6 and 6l6 tubes. I'll probably change that out for a better matched transfomer.

Title: Re: modifed 5e5
Post by: LooseChange on March 12, 2011, 07:17:42 am

Ouch!
If the master darkens as you roll it back, add a 100k resistor between the pot and the phase inverter.

Title: Re: modifed 5e5
Post by: blues man on March 12, 2011, 08:29:58 am

I am trying to understand why that would work. I thought if you put in more resistance it would darken. You are talking about adding a resistor in series with the wiper? right? I did put the 470k before the pot to tame it down a little. I still have it on the bench I may have to do that just to see what it does. Thanks for the input.

Title: Re: modifed 5e5
Post by: John on March 12, 2011, 08:57:29 am

Thanks for the schematic, and I look forward to seeing pictures as well! I think this is what I'm going to do for my first build. It seems simple enough for my simple mind to get around, but involved enough to be fun.

Title: Re: modifed 5e5
Post by: blues man on March 13, 2011, 08:13:58 am

I have posted a couple of pic's for you to check out.

Title: Re: modifed 5e5
Post by: Willabe on March 13, 2011, 02:01:20 pm

That looks great! Very nice lookin cab!


                 Brad          :icon_biggrin:

Title: Re: modifed 5e5
Post by: chocopower on March 13, 2011, 02:07:05 pm

yes, I totally agree.

That cab is really nice!

Title: Re: modifed 5e5
Post by: John on March 13, 2011, 02:26:47 pm

Sweet!

Title: Re: modifed 5e5
Post by: blues man on March 13, 2011, 04:55:31 pm

Thanks the cab is florida cypress very easy to work with. 3/4 dovetail joints then rounded off with a 1/2 round router bit. Using the bogen chassis gave me new idea's on the layout which saved a lot of wire. The master control is on the rear of chassis.

Title: Re: modifed 5e5
Post by: blues man on March 20, 2011, 03:38:04 pm

Can anyone explain to me why the master vol when turned all the way down, I can still hear my guitar coming through the speaker. I would of thought it would have grounded out the input of the pi so no signal would go through.

Title: Re: modifed 5e5
Post by: sluckey on March 20, 2011, 04:34:34 pm

The pot wiper may not be traveling all the way to zero ohms, or the ground for the pot may have some resistance. To check for either of those just connect a jumper clip lead between chassis ground and the left end of that .022µF cap connected to the wiper.

Title: Re: modifed 5e5
Post by: blues man on March 20, 2011, 08:06:51 pm

I did change the pot to a new one. the old pot had 27 ohms to ground. I also grounded the cap as you suggested and the problem still exsists. I am not to concerned about it the amp seems to be working fine. I have been making a lot of cap changes experimenting with tone. I dont know if it had this problem before I started the changes are not. I also checked the grounds and soldering. The amp is dead quiet with the volume off. I have the grounds from both the volume and the master going to the same ground buss. I also put a 100k res between the wiper and the .02 cap. good call on checking out the pot. I didn't think about the wiper not going to zero ohms.

Title: Re: modifed 5e5
Post by: DummyLoad on March 20, 2011, 10:36:47 pm

third stage with a 470K grid stopper, f-3dB is about 3.3KHz with a 1M load. if it sounds dark, this stage is likely the culprit.

grid stopper value:
with 390K  f-3dB =  4.0KHz
with 330K   f-3dB = 4.8KHz
with 270K  f-3dB = 5.9KHz
with 220K f-3dB = 7.2KHz

maybe 270K or 220k?

--DL