Hiwatt question...

[doctord02]

Hey folks... I'd earlier mentioned I was building a 200 Hiwatt style amp. I've just recently discovered the Jimmy Page preamp schematic, which looks quite interesting... It's also much closer to how I wanted to do the first stage as opposed to the other Hiwatt preamp schematics.

I have some questions... What is the "Balance" pot adjusting? Gain on the footswitch boost? Can I modify this circuit to remove the footswitch and just hardwire a value instead of using a pot there?

I dont really need a boost; the amp will mostly be used as a bass amp... Plus, my faceplates are already made and I just have to make do with them...

Here's the circuit:

http://mhuss.com/Hiwatt/Schematics/DR_Pre2InputJP.gif

Thanks for any suggestions!

Dave

[Bob-I]

Yes

[CaseyJones]

Yes

+1

Take note of two things: One, you pulled your schematic down from Mark Huss' site. Next, Mark is a moderator here. So: If Mark is really busy or he doesn't notice your post PM him. He's put a ton of work into HiWatt research which makes him the authority.

[mhuss]

The JP preamp is a bit 'gainier' than the stock one -- I'm not sure if that is what you're looking for. If you're set on building the JP/SAP preamp I'd suggest emulating minimum boost, i.e., change the 68k to a 100k, drop the balance control, and connect the 4k7 directly to ground. I'd also drop the 47n cathode bypass cap on the second stage.

On the other hand, the early 70s stock preamp is awesome for bass; For a custom build you could just skip the brilliant channel.

--mark

[doctord02]

Thanks Mark!
Nothing is carved in stone yet, so it might well be just the normal channel of the early 70's preamp... Well, having only two inputs *is* carved in stone, because of my chassis and faceplate.

If building the '70's preamp, would you just skip using the triode devoted to the brilliant channel, or would you parallel the two triodes and adjust the plate and cathode components?

Thanks for your input!

[mhuss]

I'd just use the single triode. The second stage also uses only one half, so you could combine the two stages on one ECC83.

--mark

[doctord02]

Most excellent, I cant believe I didnt notice the missing triode in the 2nd stage... That will work just fine.

Thanks Mark!

[andrew]

For the sake of adventure could the HIWATT tonestack be used in place of the Rocket tonestack?

[doctord02]

For the sake of adventure could the HIWATT tonestack be used in place of the Rocket tonestack?

Probably, but considering the Rocket was designed as an AC30 "done right", I cant say that I'd personally do it and expect any improvement... If you think about it, Hiwatts are BIG sounding, BIG octal bottle tube amps, that are by their very nature crushingly powerful loud amps. The Rocket is a more nuanced, subtle 9-pin EL84 output tube amp, more jangle, chime and shimmer...

Additionally, part of the Rocket/AC30 sound is the Cut control.

But hey, it might be worth pursuing.

[andrew]

I had an 80's HIWATT Lead 30 with 4 EL-34 that sounded pretty nice and why I let it go I don't remember (and it was only $300). Is there a schematic on it? It was a Sterling Import 1-12" combo.

[mhuss]

I'm prejudiced , but I think the classic Hiwatt tone stack is one of most versatile available, much more so than the standard Fender/Marshall style.

--mark

[gldtp99]

On the other hand, the early 70s stock preamp is awesome for bass; For a custom build you could just skip the brilliant channel.

--mark

It looks like i'll be building a Hiwatt-type bass amp for a local player---he had been using a Fender Showman for bass duties and he tried out a DR103 clone i built (w/Edcor Trannies) that's being used for guitar by another local band.
I could use the extra Sound City 120 Partridge OT i have on hand and go with EL34x6 for >100 watts.
i'll probably use the Weber WPT 100 PT i have on hand (350-0-350@400mA).
I've already built a single channel Hiwatt preamp with only three preamp tubes --- but i have faceplates on hand for the 4-input preamp so i'll most likely go this route.................gldtp99

[mhuss]

I put a Heyboer DR103-style OT in a Sound City 120 (after stealing the original Partridge ), and now it puts out 150 watts clean! I think the output impedance of these (both real and clone DR103 OTs) is a bit on the low side for 4xEL34 @ 450v.

--mark

[gldtp99]

I understand that the SC 120 OT's have 1.7k ohm primary imp. Are the Heyboer 100 Partridge clone watters about the same ?
I'm just not a fan of the SC 120's active Mk4 preamp----a couple of days ago a local player came over looking for a powerful head for his 2nd guitarist (he plays a very loud rack system w/Marshall 9200 100/100 watt power amp)---i had him try out some 50 watt amps but he wanted more power so i 1st ran him through my SC 120 TSMod head (has MV, loses Presesce control--- copied from the factory SC 120 Tour Series amps)-- he spent 30 minutes trying to dial in "his tone" with the weird active Mk4 preamp and never really got there---- but he did like the power.
Then i ran him through one of the SC 120/Hiwatt conversions and he was smiling right off the bat.
Yesterday he and his 2nd guitar player came over and tried out the head and a bunch of pedals and decided to pick it up.
Now the other guy (different band) wants something like this to use for bass--- not long ago i was complaining that nobody around here wants big, powerful heads like this anymore----- when it rains, it pours i guess.....................gldtp99