Modding a Hoffman AC30 into a Liverpool

[pompeiisneaks]

Okay so I'm looking at the board layout for the Hoffman, and all seems pretty much like stuff I can do with a bit of twiddling/changing etc, but I did have a few questions:

PT: the existing Vox Transformer I have is a Heyboer 280-0-280 at 270mA Secondary, 6.3V 6A, 5V 3A (which won't be used anymore). but the power section of the schematic for the liverpool shows 234VAC before the diodes and then 331VDC at B+1, but if I'm doing the math right, I should have about 252 after the rectifier so I'm a bit hot. Is that going to be fine? or do I need a slight dropping resistor before B+1 to get it down to the right range (Or is my math totally off, I see from the hammond rectifier doc that for a resistive load after the rectifier, its .45 X VAC Secondary (280*2) * .45 right?)
OT: The specs I seem to be seeing for the 4 el84's in the TW is like a 5.2k primary, but the Vox AC30 OT has 1850X2 (I guess htat means it's only 3700, and I'm not sure if that's going to be 'acceptable' for the specifications of this amp?

Finally, I've seen this before and can't remember 100% but it looks like 1/2 of a triode isn't used, do you just jumper pins 1-3 (schematic says use V1b only) of V1 and ground them? Is that normal process for an unused triode? or just connect them together and not ground them?


I'm likely to have a few more questions, and photos/video of the process. Hopefully it will be a full Liverpool in exacting detail, but using my own layout due to converting the Hoffman Turretboard for this use.

Cheers!

~Phil

[pompeiisneaks]

I also realize now I didn't explain the 'what/why' of the conversion.

Since I have a new Vox AC30/4 that I built, i don't really need two AC30's so I'm repurposing the old AC30 I built from Hoffman amps layouts. The questions above are about using that turret board, and the sockets, transformers, etc and just buying the differing components to make it a 100% clone of the liverpool. Hope that makes more sense about the questions.

Do we have any resident TW experts still around or have they all gone bye bye (If I don't hear back I'll still build it with what I have and see what I get)

~Phil

[M Fowler]

Your PT is fine. The usual Liverpool OT is 5k2 but I think some have used other values such as 6k6. As you know 4k is normal for most Vox type 30w/36w builds.

There are all kinds of Trainwreck builders still frequenting the forum, remember this all started in 2005 so most are past building TW amps.

Attached is Hoffman style TW Express board if that helps.

hoffmanexpress_final.gif

Hoffman Express layout.jpg

[joeboo88]

Mark: I hope you back up your files, you have a treasure trove of stuff,
and I always look forward when you give us an attachment.

[pompeiisneaks]

Very cool, thanks! I think this layout looks a bit different, but still gives me ideas. It seems like the normal channel was left in this layout as well eh? (hard to say for sure, bad eyes and small fonts )

Good to know others have done this kind of thing before.

~Phil

[pompeiisneaks]

I stand corrected, looks like one input but instead of using a V1b V2a-b type setup this ones got V1a-b and V2a only. Seems to be different from my board as well: http://el34world.com/Hoffman/files/Hoffman_AC30.pdf

~Phil

[M Fowler]

Here is another board layout which can zoom.

hoffmanexpress_cap.jpg

[pompeiisneaks]

Hmm weird still can't see them, its a little bigger but when I zoom in it looks like this:

Screen Shot 2017-03-08 at 3.26.43 PM.png

[M Fowler]

Yeah I know they are blurry.

I tried to get better images years ago but no luck.

I even contacted Doug Hoffman but he said they were not his, just Hoffman style only, Sorry.

[pompeiisneaks]

Yeah I know they are blurry.

I tried to get better images years ago but no luck.

I even contacted Doug Hoffman but he said they were not his, just Hoffman style only, Sorry.

It's all good, thanks for those, I'll post information about the build, and may create a layout for the turret board style if it seems good.

Sent from my LG-V521 using Tapatalk

[M Fowler]

Mark: I hope you back up your files, you have a treasure trove of stuff,
and I always look forward when you give us an attachment.

I replied but it is missing?

Yes I recently did a backup when my CPU motherboard and power supply failed on me.

New CPU sucks I liked XP Professional and all the software I had I can't use anymore unless I find another XP CPU.

[pompeiisneaks]

I'm adding a screenshot of a visio I've made of the 'Hoffman Style' layout I created, may not be 100% exact to the style, but it's turret board and close. Please do review and let me know if it has issues. (I'm not building this exact layout, but figured I should create one if I end up building this one again.)

Let me know if you guys see problems.


Edit: found a few errors, fixed. and made a few tweaks.

LiverpoolLayout.png

~Phil

[M Fowler]

It looks very nice, I haven't looked it over though, maybe later. Hope others beat me to it.

[pompeiisneaks]

Another question. Anyone have a good source for 130Ohm 25W resistors? I'm getting nothing on Mouser, Digikey, etc. Why does the liverpool use 25W resistors for the power grounds? seems excessive, when the AC30's I've built used 10W?

Also any insight into why the tube pairs were set to separate cathode caps and resistors instead of a single one?

~Phil