Reverting a modded 73 DR-103 back to stock. Help please!

[clothears]

Hello there!
This is my first post from sunny Tokyo. I will begin by making a disclaimer that I've only ever done a recap and a tonestack mod on an amp before, so I'm a bit green around the gills in regards to big alterations. Anyway!

I've just purchased a 73 Hylight DR-103, but the previous owner had some mods done to it, namely a strange PPIMV mod involving a stupid amount of glue gun glue, some shielded wire, a dual 1M pot and four 47nf caps in place of the two v4 47nf coupling capacitors.

You can see this mod below:




Aside from that, the 100 ohm resistor in the power amp section seems to have been replaced by a 150ohm resistor. Does anyone have an idea why? I'm not sure as to the reason why this would be done.


A final mod involves an additional resistor (dale rn-55 I think) attached to the 47k resistor in the power amp section. I'm assuming this is just to bias the tubes that are in there now, however. Could anyone confirm that?


I basically either want to get the current PPIMV out completely, or get in a replacement which would bring back the "clean machine" nature of the amp.

I thank you in advance for your guidance. (ps this is a cross post from another amp forum, but I'm hoping you guys will be of more help!)

[OldSchoolDave]

(ps this is a cross post from another amp forum, but I'm hoping you guys will be of more help!)

I can't offer technical advice, only emotional support - welcome to the Vintage Hiwatt Forum !

Hopefully, the experts will chime in soon. It'd be great to get all that glue out of the amp and get her back to original.

Dave

[clothears]

I guess in a way the mods are a good thing in that I paid a good chunk less than market value. Over here in Japan, Hiwatts go for stupid money if they become available. There are so many hi-fi audiophiles over here that nearly all the hiwatts I have seen have been cannibalised for the Partridge transformers and Mullard tubes, making a Hylight next to impossible to find.

That said, I want to revert this beauty back to stock. I've already sourced a couple of mustard caps to replace the weird blue ones that are in there at the moment.

Fingers crossed it won't be much of a hassle to fix.

[Dr.HI-TONE]

Welcome to the Vintage HIWATT Forum!
Yikes, that DR103 looks like it needs a tissue for all that gunk.

Do you have a pic showing the complete internals? I only wonder if there are more mods earlier in the preamp that increase the gain?

I would start by snipping out the extra BS and replacing the .047uf caps with original mustards, Sozo's or mallory 150's. In that order of preference. (edit. I just notice that you already have the mustards, Great!)

replace the volume pot with a 250k log or linear, either work fine.

Prof. Huss has a layout on his tribute site, follow that and you should be good to go. http://mhuss.com/Hiwatt/tech2.html

and be on the lookout for a maniac with silicon all over his hands!

[mhuss]

Except for the snot, er, I mean glue, it doesn't look too bad. The stock MV was removed and those fllying resistors put in its place, and the "blue bridges" are just the normal PPIMV stuff. Replace the 'bridges' with the 47nF Mustards and put the MV back in, and you should be good to go.

As Doc said, it wouldn't hurt to post an overall shot so we can identify any less obvious mods. The PPMIV should not affect the 'clean machine' nature of the amp, so there may be other changes.

It looks like the can caps were replaced with smaller physical units, hence the extra glue around those. As long as the values are right, should be no harm there.

--mark

[clothears]

Thanks so much guys. You've been a great help thus far.
Regarding the "clean" nature of the amp, at present if I play my guitar (HB pickups) with a fair amount of viciousness, the amp will begin to break up at about 11 o'clock on the normal channel volume control. By 1 o'clock, it becomes extremely gritty, and at 2 onwards it becomes like a distortion channel. Sadly, I've never played a Hiwatt prior to this, so I don't know what is "normal" so much... Sounds great as it is anyway, but I'd like it to be as stock as possible.

Here's the (sadly not so clear) gutshots that the seller provided me. Hope they're of help!




Caps all seem to be the right values save for the internal can replacement - The can has been replaced with two 16uf caps instead of a 32/16 setup.

[mhuss]

I'd like to see the other end of the big turret board and the surrounding area.

--mark

[clothears]

I'd like to see the other end of the big turret board and the surrounding area.

--mark

Hi Mark.

You mean the end nearest the inputs or the master volume end?

Here you can see the photos taken by the guy who sold it to me including some photos of each board:
http://photos.yahoo.co.jp/ph/jill_sherb ... .dir=/a892
You just have to click on the thumbnail, then click on the bigger picture in the next screen to get full-size pictures.

Here are (hopefully) relevant medium-size versions and links to the larger full-sive versions.

http://photos.yahoo.co.jp/ph/jill_sherb ... t&.hires=t

http://photos.yahoo.co.jp/ph/jill_sherb ... t&.hires=t


If they're not good enough, let me know and I'll take a pile of hi-res photos for you.
It's 2am here, so I won't have the photos until tomorrow.

PS Your site is fantastic! It makes for some good reading. Many thanks for the resources, and many thanks for taking a look at this one for me!

[clothears]

Ahh. Actually I just spotted a capacitor difference. The V1A / V3A plate coupling capacitors are 33uf, but "stock" is 22uf according to schematics. Post-factory mod, perhaps?

[Dr.HI-TONE]

Ahh. Actually I just spotted a capacitor difference. The V1A / V3A plate coupling capacitors are 33uf, but "stock" is 22uf according to schematics. Post-factory mod, perhaps?

good catch, that solder joints don't look very good with that cap either. I doubt its originality. Other than that, I don't see anything glaringly "off" in the early preamp area.

[mhuss]

+1, except the oddball is 33nF, .033 uF.

--mark

[clothears]

Ahh. Actually I just spotted a capacitor difference. The V1A / V3A plate coupling capacitors are 33uf, but "stock" is 22uf according to schematics. Post-factory mod, perhaps?

good catch, that solder joints don't look very good with that cap either. I doubt its originality. Other than that, I don't see anything glaringly "off" in the early preamp area.

It was the dodgy soldering which made me check the value.
Yeah I'll give that one a touch up. In fact, I may as well comb the other modded areas for signs of bad soldering.

+1, except the oddball is 33nF, .033 uF.

--mark

Hahaha. A 33uF 400v mustard cap would be the size of my fist if such a thing existed. THAT would be an easy to spot mod!

I'm guessing that all that would do is make things a fair bit bassier? How's that for circumstance! I happen to play in C standard tuning with strings like rope, so that works out rather well all things told. On the other hand, would changing them back do anything to clean up the amp?

With replacing the 250k pot; are the CTS ones decent enough?

I can pick one of these up tomorrow, or I can order some fancy clarostat mil-spec one for triple the cost.

[Dr.HI-TONE]

the CTS should be fine.

[mhuss]

+1 -- the only downside is the CTS might 'feel' noticeably different, but it will work fine. A PEC will *definitely* feel different than the stock pots.

--mark

[clothears]

Well, I'll be attempting the de-mod in a few days' time.
I'll do some photographic documentation of the process; I guess that people who wish to add a PPIMV could logically follow the reverse procedure to obtain the desired result.

I also tried to remove some of that horrible silicone stuff. It's an absolute nightmare, as it doesn't come off in big pieces. Instead, it tears off in tiny slivers. Methinks it will be a rather...annoying process. Swearwords may be heard as I'm trying to remove it from resistor leads etc.

Thank you both for your help. Once I've modded it, I'll be sure to take some decent gut shots of the whole shebang.