Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on August 08, 2010, 06:55:43 am

Title: PLEXI with TWEED OVERDRIVE
Post by: TIMBO on August 08, 2010, 06:55:43 am

HI guys, I've been inspired by the TWEED OVERDRIVE. I have my own version of the 50w Plexi with Dougs HOT SWITCH.So after the response to the Tweed Overdrive Post,and the amp requiring some much needed tweaking,i was hoping to remove the Hot Switch and insert the Tweed Overdrive.All feedback welcome.Thanks

Title: Re: PLEXI with TWEED OVERDRIVE
Post by: Geezer on August 08, 2010, 07:06:32 am

Hey Tim!

What's V2b doing? Parallel w/ V1a?

I feel sure the amp will sound great....very similar topology to Tubenit's "Carolina ODS".

G

Title: Re: PLEXI with TWEED OVERDRIVE
Post by: tubenit on August 08, 2010, 07:27:48 am

I'd definitely change two things.  I change the input resistor from 68k to 33k. 

And I absolutely would lose the 320uf on the V1-3 cathode.  You will need something like a 2.2uf or smaller or 4.7uf at the most there. A 320uf there will sound like MUD.

With respect, Tubenit

Title: Re: PLEXI with TWEED OVERDRIVE
Post by: TIMBO on August 08, 2010, 02:45:43 pm

Hi Guys, I was trying to keep it sounding more like a marshall than the Tweed and Caroline overdrive by keeping similar values and then tweak it up when i get it together. I forgot to put the hi/lo switch in.As for V1a parallel with V2b i was using the colour layout for the Tweed Overdrive which had the Fatness pot on the back panel which showed it hooked up that way (i thought it was easier that way, will it make any difference, although i did notice on another layout it was different.)Thanks   

Title: Re: PLEXI with TWEED OVERDRIVE
Post by: Geezer on August 08, 2010, 04:06:47 pm

Quote

As for V1a parallel with V2b

If you are having that triode parallel (using a separate plate resistor), then you need a coupling cap from the V2b plate to the MV.

G

Title: Re: PLEXI with TWEED OVERDRIVE
Post by: TIMBO on August 09, 2010, 02:30:54 am

Thanks for the feedback Geezer.Its these types of things that i have little knowledge of. Please make changes to the schem as i am not 100% sure of your intentsions.I tried to just insert the overdrive as your shem and layout showed. Thanks for the help

Title: Re: PLEXI with TWEED OVERDRIVE
Post by: tubenit on August 09, 2010, 05:52:27 am

I think he is talking about this. Your paralleled triode was not doing anything the way you had it drawn. It makes more sense to me (if the layout allows) to simply connect the plates together to the same plate resistor and coupling cap the way DaGeezer did.

with respect, Tubenit

Title: Re: PLEXI with TWEED OVERDRIVE
Post by: Geezer on August 09, 2010, 07:07:42 am

Yes.....that works.

Title: Re: PLEXI with TWEED OVERDRIVE
Post by: TIMBO on August 09, 2010, 01:52:44 pm

Hi guys. The more i talk about putting amps together the more i under stand. In the Tweed Overdrive schem it shows a 56k connected to pin 6-V1b a connection from V1b to pin 6-V2b(i did notice this is different to the Hoffman Layout)The sepperate connection with the 120k resistor was to maintain a similar voltage to that plate as the tweed overdrive (if that makes any sense!!!!) Thanks

Title: Re: PLEXI with TWEED OVERDRIVE
Post by: TIMBO on August 14, 2010, 04:05:08 pm

Hi guys, Thanks for the feed back on this project. I am going to need some more info on the PPIMV as i am still learning about this stuff. So if you could point me in the right direction regarding this mod.Thanks