Score ! My 1st Hiwatt ! 504

[thames]

Hello!

I just acquired a DR504, it is actually on its way home.

A '79 Hylight, with tag boards and stock components. It has been modified quite a bit, including the infamous Canadian Gain Mod and a FX loop. It works fine but I'll have to spend some time on it to bring it back to stock components. Hopefully I have a few NOS Mustard caps @home...

Does anyone have something to shard about these mods, how they affect the amp and anything I should know or care about before de-modding ?
I already have some knowledge on amps (having built 2 amps from scratch, a BFDR and SuperLead)... so I know a few basic things....

[Dr.HI-TONE]

Congrats!

[OldSchoolDave]

Nice going!

I'd suggest you live with the amp as-is before making any changes. If you don't care for the Canadian mod, it's easy to undo. The effects loop may not impact your sound at all. Just give the thing a visual inspection for bulging caps and loose joints before you fire it up.

Enjoy your "new" Hiwatt!

Dave

[thames]

Nice going!

I'd suggest you live with the amp as-is before making any changes. If you don't care for the Canadian mod, it's easy to undo. The effects loop may not impact your sound at all. Just give the thing a visual inspection for bulging caps and loose joints before you fire it up.

Enjoy your "new" Hiwatt!

Dave

Dave,

Good suggestion. I'll see if I can live with that. If I post pictures, can some of you englight me about the FXloop and its impact on tone ?
I have a good benchmark amp to compare with, a Trinity Triwatt Custom Lead, that I will sell back eventually shortly.

[OldSchoolDave]

If I post pictures, can some of you englight me about the FXloop and its impact on tone ?

There are some here who certainly can (I don't pretend to be one of them ). Post away!

Dave

[jcmh1]

Does anyone have something to shard about these mods, how they affect the amp and anything I should know or care about before de-modding ?

My advice, for what ever it is worth, is get the amp as clean as possible. You can always add pedals

I suggest you vist Mark H's web site on how to undo the Can mod.

http://www.mhuss.com/Hiwatt/index.html

There are good instructions on how to do it, and also instructions on the "so called" de fizz mod for amps of this vintage. I will be doing the same to my 79 504 this summer .... assuming i find the time. The de-fizz components can be bought as a kit from VHR

regards ... john

[thames]

Thank you so far for your kind/helpful words...

I just got the amp this morning, its a monster !

Now, take a look. There's a switch on the back that completely cuts the FX loop from the circuit. Thats good news.

Looks like the 470k from the Canadian mod is absent (from its actual location), but the yellow wire is still unattached... some strange wiring here and there.... take a look :

http://www.led-zepped.com/hiwatt504inside.jpg

[Dr.HI-TONE]

lots of weird stuff going on there. It should have loads more gain than normal. but that is all I dare speculate.

[mhuss]

Wow, lots of field-expedient-repair, flying caps and what not. I suspect all that crap around V2 is for the effects loop. None of that is irreversible.

Also looks like someone "repaired" the amp by replacing most of the original mustard caps.

--mark

[thames]

Wow, lots of field-expedient-repair, flying caps and what not. I suspect all that crap around V2 is for the effects loop. None of that is irreversible.

Also looks like someone "repaired" the amp by replacing most of the original mustard caps.

--mark

Yep, that sucks.

I'll start by restoring the preamp circuit... as the FX loop has a on-off switch, this I can disconnect it completely from the circuit.

1st problem noticed : one of the volume doesnt seem to work well... probably bad wiper or something, sound goes up and down, and the pot doesnt seem to work well...

[thames]

Well, I spent some time de-modding the amp last week... turned out pretty well, works fine now and sounds marvelous.

It appears that the yellow brick capacitors are late 70s Philips MKC 341 HQ capacitors, metalized polycarbonate, often seen in vintage audio equipments and enthusiasts. Supposedly very stable, and strong insulation resistance...

But anyway, I already ordered some NOS Mustard to replace em and bring it back to stock condition.

I'll post pictures of the work this afternoon....