vintageHIWATTconvention.com

I haven't done much with it lately. With summer here, I'm busy running around with the family, and out to the lake for weekends, so haven't had much time to play guitar or look at any equipment maintenance over the past few weeks. I'm just heading out to the lake for a few weeks extended vacation so...

Thanks Mark. Yes, the coax cables are going to both V1 and V2 are grounded at only one end - the ones to V1 are grounded at the input jacks; and the ones at V2 are grounded at the pots. At V1 and V2 just the center wires are connected, the shielding is trimmed and wrapped as it came from the factory...

Hi Mark, I finally found some time to troubleshoot some more. Here's what I found: 1) With the PI tube pulled out and everything else as normal, there is no hum, the amp is dead silent when turned on and standby is disengaged. 2) With a brand new PI tube vs the original one that was in there, there ...

I haven't tried that - you think maybe the PI tube is shot? It still has the original '79 Mullards in V3 and V4 - I replaced V1 and V2 as they went microphonic a few months back.

I'll give it a try and see if it solves the issue or not.

thanks Mark
TRJB

My '79 2-input DR-103 has developed a hum (I believe it's 60hz AC noise). Symptoms: -it's there whether I have anything in the input or not. -it doesn't change with either of the preamp volumes. -it gets louder or softer with the master volume. I should say, it amplifies and works just fine, but the...

Hi all, I know that in traditional cathode follower applications you can't use spiral filiment type tubes because the maximum cathode-to-heater rating of 100 volts is exceeded, which causes them to fail very quickly. This rules out anything (current production) from New Sensor for that position on a...

It still has the factory original Mullards in the preamp. They were tested by the tech who did the recap for me a few months ago, and he said they are pretty much as-new. In hindsight, I don't think any additional mods are required ... I was following conventional logic when trying to dial in a good...

Thanks Mark, that's what I was thinking... I plugged the Marshall values into the online cathode bypass calculator at ampbooks.com, and then the Hiwatt values, and it looked like a total capacitance in the range of 1000n to 1500n would give me a frequency curve and gain very similar to the the Marsh...

Having continued to play with the "OL" version of my DR-103 for a few weeks now, while it is vastly improved IMO from the pre-mod version, I'm still finding it a bit brighter than I would like, and without adding any radical additional mods, I think I understand from some research that by ...

I have a 1979 2-input DR103, Canadian Import. Back in '79, the distributor removed the voltage selector and hardwired it internally with a jumper across the selector pins for the 117v option, applied the orange "Ontario Hydro" approval sticker, and wrote "375W" on the back near t...

So finally, after *months* of mental labouring over what to do with my amp, I did what I posted as Option #3 above: 1) removed the "Canadian Mod" 2) added the 470k x 2 resistors (resistive mixer) for Normal and Bright channels 2) installed the extra 2 resistors and capacitor at V2 to add t...

Strange, because the 68k resistors are NOT shown on the schematics on your page for the late 70's 2-input models, or on the schematics Biacrown 80's models, and also on the AudioBrothers schematics (both the 19/05/95 and the c.2001 versions). And also none shown on the schematic for your own 504OL o...

Thanks Mark. The "cloud" just indicates that the coupling cap was changed, but I don't know if it was raised or lowered in value since I only saw these 2 photos. I also note that all of the 60's and up to the mid-70's 4 input preamps had 68k grid resistors on V1, but then in the late 70's ...

Hi, I found these pics of a vintage DR103, it has 3 subtle mods that I can see in the photos, and as indicated on the schematic: 1) There is a capacitor installed across the V1A plate load resistor (value unknown) 2) The V1A coupling capacitor appears to have been changed, but the value is not known...

Beyond that, from the photo on Kijiji, this amp appears to have some kind of additional non-factory high-gain mod based on the extra flying components around V2, and the extra coax cables that go from V2 to V1, and also back to the input jacks. Hard to tell exactly as the photo is not very high res,...