Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: whalecalls on June 15, 2020, 05:28:31 pm

Title: Installing a Hiwatt Fixed Bias Inverter in a Marshall 2204ish amp
Post by: whalecalls on June 15, 2020, 05:28:31 pm

Greetings,
    This is my first post here on this wonderful site. Quick question. Has anyone here ever tried building an amp with a Marshall-esque topology, but with a Hiwatt style PI? There are things that I love about Hiwatt and Marshalls and I'm wondering if it would be possible to get the best of both worlds. I love Hiwatt for the pure power that they have and for being an amazing pedal platform. They have a very "direct" sound and feel which I dig, however, they can be a bit sterile/neutral tonally. I know there's a lot of factors why hiatus have so much power (high plate voltage and those wonderful trannies), but I'm thinking a big part is that the PI doesn't distort a ton which makes it so great for pedals. I love my "Marshall", but I wish it had a bit more headroom to keep up with the DBS from my fuzzes and boosts like hiwatts do.
     Long story short.... Has any one put a Hiwatt PI in a Marshall 2204 style amp or has any built a dr504 with a predominately Marshall preamp? Thanks y'all.

Title: Re: Installing a Hiwatt Fixed Bias Inverter in a Marshall 2204ish amp
Post by: shooter on June 15, 2020, 06:28:30 pm

welcome

I consider the pre "it's own thing", the PI and PA the "other thing", they stitch well regardless of brand, just your effort  :laugh:

Title: Re: Installing a Hiwatt Fixed Bias Inverter in a Marshall 2204ish amp
Post by: whalecalls on June 17, 2020, 11:00:55 am

Thanks Shooter,
     Yes, I'm sure it would work, but I wonder if changing the PI in a Marshall would dramatically alter its tone and/or give it some more headroom. I will try this out someday and posts. Thanks for the response! Cheers

Title: Re: Installing a Hiwatt Fixed Bias Inverter in a Marshall 2204ish amp
Post by: pdf64 on June 17, 2020, 11:47:49 am

I don’t see any big difference between the Hiwatt and Marshall LTPs? It’s not an apple and oranges thing. So no reason to expect a significant difference in performance.
Note that the Hiwatt isn’t fixed bias, it’s just a different arrangement of self bias. The difference is that the grid is referenced to a particular % of the HT, rather than the LTP’s tail.

Title: Re: Installing a Hiwatt Fixed Bias Inverter in a Marshall 2204ish amp
Post by: whalecalls on June 19, 2020, 03:40:25 am

PDF,
    Yeh, forgive me and my limited knowledge especially with PIs. Interesting about the grid differences. I will probably just experiment and see what happens. Thanks for the info!