Harry Joyce amp gut shots?

[Emiel]

Anyone own a Harry Joyce 50 or 100 watt and willing to share some gut shots?

Interested to see what makes/made these amps different from your average Hiwatt.

[JD0x0]

Following. IIRC the original Hiwatts, while wired beautifully, have grounding flaws, for example. I wonder if the HJ amps improved on that.

[Emiel]

Mark Huss has some on his website:
https://hiwatt.org/ipage.php?n=13

I think these are all 'early' HJ's. These seem to be based on the '80s Hiwatt 'OL' with some minor changes. The resistor over V2 is for instance 1K5 instead of 47K, therefore reducing most of the extra gainstage.

The newer HJ's (post-Harry) supposedly have some modifications that make them a bit more different. I have yet to find some clear shots of the pre amp board...

[Roe]

Following. IIRC the original Hiwatts, while wired beautifully, have grounding flaws, for example. I wonder if the HJ amps improved on that.

I suspected this - could you elaborate?

The HJ amps got a gainstage more than most (not all) hiwatts. They are based on the gainier 80s amps

[Roe]

HJ just tweaked the early 80s lead circuit. it seems that the two 47nf coupling caps on 100w PIs were replaced with 4 22nf caps - one for each el34:

"Although many people believe that these are the same, there are some major differences in sound and design. Besides the fact that Hiwatt amps underwent many changes throughout their production years themselves, which changed the sound. Harry Joyce amps were actually the product of all the changes made. Originally Hiwatt amps came with .047mf coupling caps versus the Harry Joyce .022mf best known as the “Marshall Value”. This gave the amp slightly less bass, but this was compensated in the first stage by means of introducing a 150mf cathode bypass cap. Early Hiwatt amps on the other hand used a .047mf in the Brill input, and none in the Normal. Another change was made to wire the first preamp tube cathodes together, where the original resistors were 2.2K each now both cathodes were summed through a 1.5K resistor and a 150mf cap across. The second stage on Hiwatt amps used only half of V2. Harry Joyce amps use the whole tube by cascading the inputs of V2a, and V2b for more gain. The bias feed resistors changed from the 100K to 220K. This resulted in a more aggressive sound, and unlike the older Hiwatts that had two preamp to poweramp coupling caps (.047 mf one for two tubes along with two 22K resistors for the 100Watt version) the Harry Joyce doubled up in terms of having four .022 caps with four 22K resistors.The idea behind was to make the amp more stable, and balanced. Additionally the Harry Joyce amps had no bias adjuster, because according to Mr. Joyce the old Mullard EL 34′s were so consistent that it was not necessary. Nowadays it might be most important. Early Hiwatts came with the grids of the phase inverter V3 (12AT7!!) wired together to the cathode resistor of V4b through a 100K resistor. This design was later changed to a 220K resistor. This change gave the amp less responsiveness and sounded not as full. Power and output transformers changed from Partridge to a custom wound type, and the 100Volt output tap on the ohms selector got omitted." (http://harryjoycerocks.com/shop/?p=491)

Pics: http://ampgarage.com/forum/viewtopic.ph ... 38c7603215
See also https://vintagehiwattconvention.com/for ... yce#p16662

[wyatt]

This was a early promotional display that was recently sold on Reverb.

[Emiel]

HJ just tweaked the early 80s lead circuit. it seems that the two 47nf coupling caps on 100w PIs were replaced with 4 22nf caps - one for each el34:

"Although many people believe that these are the same, there are some major differences in sound and design. Besides the fact that Hiwatt amps underwent many changes throughout their production years themselves, which changed the sound. Harry Joyce amps were actually the product of all the changes made. Originally Hiwatt amps came with .047mf coupling caps versus the Harry Joyce .022mf best known as the “Marshall Value”. This gave the amp slightly less bass, but this was compensated in the first stage by means of introducing a 150mf cathode bypass cap. Early Hiwatt amps on the other hand used a .047mf in the Brill input, and none in the Normal. Another change was made to wire the first preamp tube cathodes together, where the original resistors were 2.2K each now both cathodes were summed through a 1.5K resistor and a 150mf cap across. The second stage on Hiwatt amps used only half of V2. Harry Joyce amps use the whole tube by cascading the inputs of V2a, and V2b for more gain. The bias feed resistors changed from the 100K to 220K. This resulted in a more aggressive sound, and unlike the older Hiwatts that had two preamp to poweramp coupling caps (.047 mf one for two tubes along with two 22K resistors for the 100Watt version) the Harry Joyce doubled up in terms of having four .022 caps with four 22K resistors.The idea behind was to make the amp more stable, and balanced. Additionally the Harry Joyce amps had no bias adjuster, because according to Mr. Joyce the old Mullard EL 34′s were so consistent that it was not necessary. Nowadays it might be most important. Early Hiwatts came with the grids of the phase inverter V3 (12AT7!!) wired together to the cathode resistor of V4b through a 100K resistor. This design was later changed to a 220K resistor. This change gave the amp less responsiveness and sounded not as full. Power and output transformers changed from Partridge to a custom wound type, and the 100Volt output tap on the ohms selector got omitted." (http://harryjoycerocks.com/shop/?p=491)

Pics: http://ampgarage.com/forum/viewtopic.ph ... 38c7603215
See also https://vintagehiwattconvention.com/for ... yce#p16662

Thanks Roe, I saw your post in an earlier topic and that one kick started my interest in these amps.

So much in fact, that I actually found pictures of a few examples and made a schematic based on Mark Huss' OL504. I had a friend modify my CP103 clone to the HJ specs. It actually sounds great, seems more balanced and rounder than a regular DR. A bit more pre amp gain too.

@ Wyatt, 1993! That is real early. Thanks!

I think I've got the early HJ schematic sorted, now I'm looking for pics of the later ones (post Harry's passing).

[Roe]

could you share a schematic of the early HJ circuit?

[Emiel]

Here you go.

[Roe]

Here you go.

great - thanks! (although the 1k5 on v2 seems wrong)

[Emiel]

You think so? Here’s an example, isn’t the resistor a 1K5?

https://hiwatt.org/pix.php?p=HJ50bGuts1

[JD0x0]

Here you go.

great - thanks! (although the 1k5 on v2 seems wrong)

On paper, that'd have like no gain and even less bass.

Honestly, no reason not to run a trimmer there, and adjust the coupler to keep a similar bass cutoff to the original circuits. The OL amps had a pot labeled 'Overdrive' I believe 500k, but a 100k would probably be better suited to the Hiwatt vibe, unless you're looking for a good bit of gain and distortion on tap. Also, personally, not a fan of the 47nF cathode bypass caps.

[Emiel]

On paper, that'd have like no gain and even less bass.

Honestly, no reason not to run a trimmer there, and adjust the coupler to keep a similar bass cutoff to the original circuits. The OL amps had a pot labeled 'Overdrive' I believe 500k, but a 100k would probably be better suited to the Hiwatt vibe, unless you're looking for a good bit of gain and distortion on tap. Also, personally, not a fan of the 47nF cathode bypass caps.

There is an extra gainstage on V2 (resistor and capacitor). I'd say there is just a little bit more gain in my amp compared to a regular DR103.

[Roe]

sounds plausible, but see here :https://www.ampbooks.com/mobile/amplifi ... alculator/

[Emiel]

Interesting... so my schematic might not be fully correct then?

I based it on the two 50 watt models found on this website :
https://hiwatt.org/ipage.php?n=13

This one as well:
https://ampgarage.com/forum/viewtopic.p ... 38c7603215