vintageHIWATTconvention.com

Hello all. As I said in my "Introducing myself" post, I have recently acquired a 1980 DR-504, serial# 14947. The previous owner said the last time he played it many years ago, it made a buzzing noise and quit, and never got around to fixing it since then. I have an Accurate Instrument Co. Tube Tester Model 257 (consumer-grade, good for testing go/no go) and the power tubes tested at about halfway up the "good" section of the meter, and no shorts. Two of the preamp 12AX7s (er... ECC83s, sorry) were bad/borderline, lucky I have two rattling around in an old abandoned project that tested good. The caps look meh... could be bulging, could be simply old, I'll replace them before I go flipping the thing on. I discovered Mark Huss' page that proved invaluable for schematics, but the signal path for this amp looks different from schematics he has posted; at first glance, it resembles a "Late '70s 2-input" AP up front with "Bright" and "Normal" inputs, but it doesn't use the second triode of V2, like the SAP schematics show. Also, it has the "Canadian Mod".

What I plan to do:
- Clean it up (mostly already done)
- Re-cap with ARS caps (best I could find that didn't involve highway-robbery-level shipping charges, and had all the exact values)
- Flip it on and see how it roars (or not)

Questions:
- I noticed it doesn't use grid stopper resistors at V2 or V3, would this be recommended? Or does it sound just fine without, especially on higher-gain settings? It's an easily-reversed mod.
- The Partridge stickers came off the transformers as I was cleaning them up, due to the glue drying out. Any recommendations on what kind of glue to use to stick them back on?

I'll post more questions as I think of them, and I'll let you all know how it goes as soon as I can get new caps. I also took the liberty of modifying Mr. Huss' schematics to show how this one is laid out; see below:

I wouldn't worry about the grid stoppers until you try it out and see what it sounds like. I am not a fan of the CMod, it was a quick and dirty hack and sounds like it.

I have no advice to offer on glue.

Ha! Yes, I should see how it sounds first. My pedigree is in the heavier genres, so I'm only hoping for enough grit to work with. Without grid stoppers, I imagine it can get a bit "spitty" at higher-gain settings, so that was my idea to smooth things out without losing grind.
For the sticker glue, I think regular spray adhesive might do the trick, or maybe double-sided tape.
Also, genuine Fane cabs won't be within my budget anytime soon, has anybody found a "close enough" sound-alike? I read on another forum somewhere that "hi-fi" speakers would be closest, but I have no idea. All I have at the moment is a 12-inch 100W Carvin "British Series" that I got for cheap at a second-hand shop and built a cab for. I'm not rich enough to be picky.

Hello,
Regarding gluing the stickers back on:
I can't say for certain as I haven't tried this method myself, so full disclosure about trying at your own risk.
I have had surprisingly good luck with plain old white PVA "Elmer's" -type glue in the past for similar projects.

I like that it isn't solvent based or too aggressive, which I would worry would attack the label and or transformer varnish.
The PVA -style glue should be mild enough you don't need to worry about it reacting too crazy.
Just a very thin smear should do it, and blot off most of the excess before it sets. Just don't get carried away as it is water-based, but a small drop or two should do the trick I would think.

Option 2:
I have seen "reproduction" Partridge labels on Reverb from time to time. Can't vouch for the quality/appearance as I've never seen them in hand, but it may be worth looking at as well. Good luck!

Thanks for the suggestion, I thought of that too, but I was worried that the glue might not be "sticky" enough, and that kind of glue does dry out over time. But then again, so did the original glue, LOL.

If you're more into heavy, the speaker you've got might be OK. Again, try and see.

Yes, the white glue isn't as "aggressive" as some other adhesives.
Worst comes to worst, you can always re-glue the labels back on if they fall off again a few years (or decades) from now!

Other options may be found at luthier supply houses:
-hide glue
-fish glue
Both are water soluble, dry clear and hard, and are fairly forgiving/easy to use.

(If it were my amp, I would avoid using a contact cement or rubber cement as these are solvent-based, and may react with/damage your label, and the original varnish on the transformer laminations. I have not had success with the "low-VOC" type contact cements, either. Waste of time and effort. )

mhuss wrote: ↑Fri Dec 15, 2023 5:03 pm If you're more into heavy, the speaker you've got might be OK. Again, try and see.

Good to know, thank you. At this point, I'm going to have to wait for a tax return to get new caps, so it won't be for another month or two. Can't wait!

elcapitan wrote: ↑Fri Dec 15, 2023 5:19 pm Yes, the white glue isn't as "aggressive" as some other adhesives.
Worst comes to worst, you can always re-glue the labels back on if they fall off again a few years (or decades) from now!

Other options may be found at luthier supply houses:
-hide glue
-fish glue
Both are water soluble, dry clear and hard, and are fairly forgiving/easy to use.

(If it were my amp, I would avoid using a contact cement or rubber cement as these are solvent-based, and may react with/damage your label, and the original varnish on the transformer laminations. I have not had success with the "low-VOC" type contact cements, either. Waste of time and effort. )

I don't have easy access to hide or fish glue, and I have a pretty tight budget, so white glue it is. Thanks for the tip, I'll be doing that sometime soon while I wait for funds for a re-cap.

OK, I've tried to post 3 times, but the website times out on me every time, so I'll keep this one short and sweet, with no pictures.
Got new capacitors.
One power tube kept red-plating, so I got a new pair.
Sounds great, but not what I need, will be selling.
The end.

Maybe if I'm in the mood later, I'll try and make a longer post, but this has frustrated me to no end today. Good night.



P.S. White glue stuck down the stickers just fine. Thanks for the tip!