Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: beckspeed on July 10, 2017, 07:44:14 am

Title: 3 Questions: 5F4 Tweed Super
Post by: beckspeed on July 10, 2017, 07:44:14 am

I'm still monkeying with this 5f4 Tweed Super (the one that was someone else's kit and I'm resurrecting). You guys were a ton of help a few weeks ago and I really appreciate it. I just added an SPDT output impedance selector switch, since the OT (classic tone 40-18105) it has a multi out. I don't normally crank it above 5-6 but I was putting it through the paces and noticed once I get to full volume (8-10) the amp gets very distorted - in a bad way. Sounds farts out, all loose and messy - not a tight "good" distortion. Tried with several guitars (single coils and humbuckers) with the same basic issue. I turned the "bass" and "mid" pots all the way down and the issue persists (albeit slightly diminished).

Previous thread for background on the amp http://el34world.com/Forum/index.php?topic=21955.msg233350#msg233350 (http://el34world.com/Forum/index.php?topic=21955.msg233350#msg233350)

here is how I wired the switch - except I left the NFB on the jack - not to the switch, because the wiring above is to switch to add an extension cab.

(https://www.premierguitar.com/ext/resources/images/content/2016-04/BLOG/Jun-16---Ask-Amp-Man/Image-3_June2106_PG_CLM_Ask-Amp-Man_Pro-Jr-switch-wiring-Fig-2_WEB.jpg)

1) Would the NFB at the jack cause this issue?
2) Other issues I should look for?
3) You guys mentioned it would help if I created a schematic for this exact amp - since its a bit of a homebrew/ hodgepodge "5F4". What program do you use to create the nice clean layout diagrams?

As always, thank you in advance!

Title: Re: 3 Questions: 5F4 Tweed Super
Post by: shooter on July 10, 2017, 09:52:09 am

1. did you run it to 10 before the switch?  once you get to a certain point, NFB can't make up for the amount of distortion you create.

2. you changed guitars, change speakers

3. http://el34world.com/Forum/index.php?topic=590.0 (http://el34world.com/Forum/index.php?topic=590.0)
This is what I use, it's free :laugh:
The "gold standard" costs more, Visio and the guys that use it create nice works, us .sch guys can do pretty well though :laugh:

Title: Re: 3 Questions: 5F4 Tweed Super
Post by: beckspeed on July 10, 2017, 10:35:14 am

Thanks Shooter - yeah I ran it at 10 before  - sounded pretty good. Warm fendery overdrive sound.

Have not tried different speakers - but I'm using my known-good go-to cabinet. I do have another I'll try though.

What about this for the layout: DIY LC? http://diy-fever.com/software/diylc/ (http://diy-fever.com/software/diylc/)

Title: Re: 3 Questions: 5F4 Tweed Super
Post by: shooter on July 10, 2017, 11:15:27 am

Quote

yeah I ran it at 10 before  - sounded pretty good.

then you know where to start looking :laugh:

any tool that gets you good results and doesn't cause high blood pressure use.
I started using pc express in the way back days, for schematics I can churn all day, for layout, that takes some Zen to keep the BP down :laugh:

Title: Re: 3 Questions: 5F4 Tweed Super
Post by: beckspeed on July 10, 2017, 01:37:33 pm

Thanks shooter - I'll start my investigation there.

Title: Re: 3 Questions: 5F4 Tweed Super
Post by: beckspeed on July 15, 2017, 09:44:39 am

so I undid the Output switch and put back at straight 4ohm output, but the blubbery distortion over 8.5 seems to persist. I mapped out the circuit. Do you see anything here that could be the cause of my issues?

Thanks

link to full size PDF http://beckspeed.com/blog/wp-content/uploads/2017/07/MK-SUPER-WD_ab_2_Flat.pdf (http://beckspeed.com/blog/wp-content/uploads/2017/07/MK-SUPER-WD_ab_2_Flat.pdf)