Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on February 20, 2021, 08:56:37 pm

Title: BIG AMP
Post by: TIMBO on February 20, 2021, 08:56:37 pm

Hi guys, I'm back.
Finish moving house, took 1500kgs of stuff to the dump that was just Not going to fit in a Townhouse.
The "MANOOK" is just about sorted.
My plan now is to complete some of my builds that need tolexing, faceplates and a bit of tweaking.
With the Xmas break putting the faceplates on hold, the Supro faceplate was ready for pickup.
https://www.guitargear.net.au/discussion/index.php?topic=50840.0


(https://i.imgur.com/3qOTrs7.jpg)
OH no, something was not quite with it........... It was much LARGER than it should be
It should be 520mm x 72mm
But it's 830mm x 120mm :yikes: :wtf
Something has gone wrong with the sizing.


Anyway got it sorted new plate made and a spare (rather large plate) put aside.
This is where the "BIG AMP" comes in.
A head style cab will be constructed Approx. 850mm long 200mm high and 300mm deep, compared to a BAEZ head i have that is 720mm x 220mm x 300mm.




(https://i.imgur.com/rLq7Jqf.jpg)
The above Supro was it's original destination, so I am going to use the preamp design as it fits the plate.
Being a LARGE build I was thinking a LARGE output is in order
I have a 100w transformer set that came out of a Eminar PA head.
OT primary 1.7k


Just need to marry the preamp to a power amp circuit.
Input welcome.

Title: Re: BIG AMP
Post by: TIMBO on March 01, 2021, 04:38:48 am

Hi guys, I think I've been able to mash a circuit together that will fit the faceplate.
(https://i.imgur.com/GNZRW20.jpg)
The JTM45/100 seems to to be hot topic ATM and I was able to score a quad of JJ KT66 cheap.
Did some test on the OT I have and the Primary Impedance is just under 4K
Keeping the Marshall feel the second channel is from the 18w

Title: Re: BIG AMP
Post by: pdf64 on March 01, 2021, 05:43:08 am

Have you considered using the ‘U’ section of a 12DW7 as the reverb driver?

Title: Re: BIG AMP
Post by: PRR on March 01, 2021, 11:55:48 am

Channel 1 has about 5 times twice the gain of channel 2.

They are out of phase and if mixed will tend to cancel.

Do you really want NFB injected at the top of the tail resistor? 

Title: Re: BIG AMP
Post by: TIMBO on March 01, 2021, 01:37:34 pm

Thanks guys....
PRR,
Feed back resistor noted.
I'm open to suggestions for the 2nd channel.

Title: Re: BIG AMP
Post by: shooter on March 01, 2021, 03:47:22 pm

Quote

out of phase and if mixed will tend to cancel.

short of adding an inverting stage, you're sorta stuck

Title: Re: BIG AMP
Post by: TIMBO on March 01, 2021, 06:38:54 pm

Thanks shooter
I’m now thinking another Marshall preamp to even it up

Title: Re: BIG AMP
Post by: tubeswell on March 01, 2021, 08:56:12 pm

Here are some 2-channel input and output ideas I put up a month or so ago. Can't remember if it was on of your threads or not Tim, so here it is again.


One of these is the same as your 2-channel input. One of these doubles as a 2-channel 'recovery' and 'mixing' stage that uses a 10k blend pot to vary the amount of half boost gain that each channel gets to feed to the PI. So you could just put whatever tone controls you want in between

Title: Re: BIG AMP
Post by: TIMBO on March 04, 2021, 02:30:07 am

Thanks mate, I'm leaning toward having two separate channels because the distance between each input is quite big.
So by having two valves as inputs would make the distance shorter from the input jack.

Title: Re: BIG AMP
Post by: TIMBO on March 06, 2021, 01:56:17 am

Hey guys,
Rather than building it and finding it won't work I have plan
(https://i.imgur.com/IsDzDjy.jpg)
Similar circuits one dark and gainy and the other bright, could be a good mix.......
Also, the old saying "if it's too good to be true, it probably not true"
I purchased a quad of JJ KT66 valves from a local supplier through ebay for $89.
A couple of days latter i get a refund and sorry we don't have any of those.

Title: Re: BIG AMP
Post by: sluckey on March 06, 2021, 07:55:34 am

Hey, Timbo. Rather than 3 input jacks you may like this idea...

     http://sluckeyamps.com/phoenix/phoenix.pdf

Title: Re: BIG AMP
Post by: TIMBO on March 06, 2021, 02:47:42 pm

Thanks mate, Just wanting to fill the holes in the faceplate.
The other little hole I need to fill is the Modern/Vintage switch, this switched between SS and valve rectifier.
The PT is a voltage doubler so a valve rectifier can't be used.
Any thoughts on a switch that will give a modern/vintage feel to an amp, Maybe increasing the HT filtering?

Title: Re: BIG AMP
Post by: TIMBO on March 22, 2021, 04:20:05 am

Hi guys, A bit more tweaking of the schematic...
So two iconic circuits, again one dark and one bright.
(https://i.imgur.com/E2hTKWx.jpg)
Another job the tackle, the Modern/Vintage switch....
Diode clipping, thoughts.....

Title: Re: BIG AMP
Post by: TIMBO on March 24, 2021, 04:13:40 am

So this what the chassis looks like...
(https://i.imgur.com/YXVExPQ.jpg)
(https://i.imgur.com/qsDUu0q.jpg)
(https://i.imgur.com/8Aw2o83.jpg)

Title: Re: BIG AMP
Post by: TIMBO on March 30, 2024, 11:38:27 pm

Hey guys,
This one has taken a another direction.
I like the 2144 sound so I've grafted the preamp to the power amp.
(https://i.imgur.com/jFJ9OLj.jpg)
(https://i.imgur.com/sqcxFOX.jpg?1)
(https://i.imgur.com/soGfv5J.jpg?1)
(https://i.imgur.com/zJCfjl4.jpg?1)

Title: Re: BIG AMP
Post by: Ronquest on March 31, 2024, 02:06:58 pm

I'm here for the last few months thinking, I need to build a new amp.  I see this post and and think, Timbo goes from design to faceplate mess-up to new design with messed up faceplate multiple revisions and then builds the amp in a few days......I'm feeling pretty lame, then I notice the dates March 22, 2021 to March 30, 2024. 

I don't feel so bad now.  But really, I need to build an amp, so many plans and no commitment.

Title: Re: BIG AMP
Post by: acheld on March 31, 2024, 06:18:42 pm

Don't over think this.   

Pick a direction and go with it.   If and when you decide you want something different, you can mod away to your heart's content.

I have a couple of amps that have been built, torn apart, rebuilt to different specs several times . . . Yeah they may not look great, but they do sound good.  Lots of fun to change direction. 

Title: Re: BIG AMP
Post by: TIMBO on April 28, 2024, 04:40:12 am

Cabs made....
(https://i.imgur.com/9Ef8udB.jpg)
(https://i.imgur.com/9CyL1dl.jpg)

Title: Re: BIG AMP
Post by: tubenit on April 28, 2024, 09:17:45 am

I always appreciate and enjoy your fine creativity and craftsmanship with your builds!  Great job!


Thanks for sharing!    With respect, Tubenit