Trying to Match a Hammond PR-40 PT to a Twin Project;>/(Hot Shot 48 Plexi)

[DummyLoad]

there is an error. input from MV-2 to LTPI .022 coupling cap - the wire from the top of the 1M to .022 needs to go the bottom of the .022 cap not the top of the .022 cap. feed from pin 2 of MV goes to top of .022 cap


- i'll fix it tonight when i get home.

--pete

[Platefire]

Yeah I missed that, glad you caught it, not too bad, just more one wire. Also what happen to the 47p between the grids right after the PI? Platefire

[DummyLoad]

corrections. please see attached. 
- added 47pF cap.
- corrected LTPI input wiring.
- power to V1 plate load resistors.
- connection points to V1 plates on ckt. bd.


--pete

[DummyLoad]

rev. 3 - third time's the charm, eh? :p


- moved the node D cap closer to V2. cleaner layout. also, V3 wiring is more tidy.
- moved the .1uF presence pot cap that's connected from wiper to GND off board to pot.


--pete

[Platefire]

Good, Thanks! Was able to print it out using poster setting and got a 3 page 8 1/2 x 11 mosaic full scale that I can scotch tape together and make a drilling template. I notice your board is 3" wide and all I've got from Doug is 3 1/4" wide--can he make it 3" wide? Platefire 

[DummyLoad]

Good, Thanks! Was able to print it out using poster setting and got a 3 page 8 1/2 x 11 mosaic full scale that I can scotch tape together and make a drilling template. I notice your board is 3" wide and all I've got from Doug is 3 1/4" wide--can he make it 3" wide? Platefire

i just checked the catalog: doug's boards are 3-1/8" wide & he won't cut any other width.  i used 3" since that made dimensioning easier for me. i revised the drawings (rev 3a) and made the board 3-1/8" - 3.130" is close enough! :-) rev 3a drawings attached.

if you have a kinko's nearby, they can print 11"x17" for you. down the road you can get an A2 size printer fairly inexpensive: such as this one.

--pete

[Platefire]

Just when I think it can't get any better, it gets better! I'm not going to comit that this is the final version but I went ahead and made a template. I can drill with this! 

Think things are firming up to order some more parts.   

Thanks for all the great help! Here is a pix of my template. Platefire

[Willabe]

Hey now, that'll work. Very nice. 

[DummyLoad]

you're  most welcome. hope it works well.

--pete

[Platefire]

In the process of going through my existing inventory to see what I got that I can use and what I need to order.

IMH0--if the schematic calls for an .022 coupling caps and you got some .025 or calls for a .1 and you got a .15----to me that's close enough and is not going to make that much difference other than leaning darker than brighter and in my case a hair darker is good! Is that copasetic?

[sluckey]

yes

[Platefire]

Thanks for seconding me, amendment passes!

[Platefire]

I've got some diodes that looks similar to Doug's "B"1N4001 is size but all I can read on it is "V2N"?
I can't find anything on the net that identifies Trying to determine if this will work for my bias circuit. Platefire

[Paul1453]

I don't know about your diodes, but I got 100 1N4007s from China for $.99 including shipping.
I think one of those might be OK in the bias circuit.   

I don't know how those commies manage to do that for $.99?   

[Platefire]

Well at 25 cents each, guess I'll just throw one in my order to Doug to be sure.

Also on EL34's, if your wanting to lean more to a Marshall Crunchy breakup sound than a clean sound--what EL34 is best budget minded. I've read the the EH tends to be better than a JJ for the Marshall sound. Platefire

[sluckey]

I've got some diodes that looks similar to Doug's "B"1N4001 is size but all I can read on it is "V2N"?
I can't find anything on the net that identifies

Throw them away if you cannot determine the ratings. They may not even be rectifier diodes! There is a wide range of diode types and ratings that all use that same body style. Could even be a trigger diode or diac.

Throw them away!

[Platefire]

OK, I've been busy with other stuff. Trying to pick up where I left off. I'm wanting to do cutting and drilling for cover plate and drilling for transformer holes. We last talked about transformer arrangement in post #115 & 116. So in reference to that I have took attached pics with that in mind, with a couple of exceptions. Since we are now using SS rectification, I arranged the cover plate to cover the two tube rectifier holes. Had to put the choke right up against the cover plate edge that was about 1 3/4" from the PT, so I also left a 1 3/4" space between choke & OT. May be a little to spread out now? So whutadouthink? Platefire

[DummyLoad]

looks good. :-)

--pete

[Platefire]

OK, Thanks DL! I will go with that. Platefire

[Platefire]

A little progress. Having to prep this old chassis to bring it around. Not going to concentrate on building the circuit until I see everything is in order on the chassis for mounting and fitting everything in--once that's clear I'll proceed with electronics. This chassis looks so rough I think it would classify in the Steam Punk category:>) This chassis was given to me when an amp building friend cleaned out his surplus junk and gave it to me. He sometimes post here as Wooley. This is an explanation of attached pictures:

1 & 2-Where the input jack needed to go was a large hole, too large for an input jack. I built an aluminum cover plate to cover it and drilled a new input jack hole. Had to scoot it over to the left as much as possible to make room for the DPDT midi switch(hot shot) between the input and pre vol. A outside and inside pix.

3-Marked chassis cover plate for mounting that huge PT. Will be using 1/4" mounting bolts on that. The sharpie marks are where the 1/4" bolts go and the large holes is 5/8" Dia to match PT wiring holes that will have grommets.

4-The small rectangle marking pix is where the IEC receptacle will go. I had to flip it vertical because of lack of space between the heavy 1/2" thick alum chassis end plate and the fuse holder.

Even though I'm taking my good time on this, I am looking very much forward to one day soon firing it up. I think once I get the chassis preped and ready it will go faster. Platefire 

[DummyLoad]

ahhh progress!! 


my notes so far: with cascaded V1 (aka the 2204) my breadboard amp is typical JCM800 sounding even with this output stage. it breaks up about the same. IMO, overall it sounds better with the bassman/JTM/plexi preamp.


--pete

[Platefire]

pete

Yeah, I'm not familiar with what a typical JCM800 or a JTM Plexi sounds like. You have to realize, I've never played over a Marshall before. That's what I'm wanting to discover! So when you you say it sounds better, I'm wondering in what way?? When you say it sounds better with the bassman/JTM/Plexi preamp are you referring to the particular circuit attached or something else??? Platefire

[Platefire]

Well pete

Guess it's no big deal. If I don't like the way the 2204 pramp sounds, it would be easy enough I think to change it to the JTM bassman preamp and try that. Guess I'll go with the established plan first and go from there. Tweak it Babe, Tweak it! Thanks, Platefire


BTW-since you are very familiar with the PR-40 power supply, I will be using 600V filter caps, do you think it would be safe to install a standby switch. The hole is already there. If I don't use it, I'll have to plug it:>)

[DummyLoad]

do you think it would be safe to install a standby switch.

sure.

--pete

[DummyLoad]

fairly concise history on the many models of marshalls and schematics in link below:

http://www.drtube.com/en/library/schematics/69-marshall-schemas

the 2204 (50W) and 2203 (100W) later become the JCM800 series, are a completely different animals from JTM45/50 models. V1 is cascaded and a master volume added after the tone stack. amp has 2 inputs: high and low - the low input bypasses the 1st gain stage. these are the most dominant marshalls from 1975 through the 80's.

--pete

[Platefire]

Yeah, since I started building this Marshall type circuit I'm learning a lot about Marshall models numbers/names. Also have read some history. Pretty interesting. Guess I'm wanting to taste a little Marshall glory in a little less wattage. I'll have to wait until the wife is gone to really give it the real test when it's finished.

I got a local amping buddy that lives about 40 miles away and we talk several times a week. He just bought a Germino JTM 100 clone$$$$ I will attach their link but they are very meticulous about re-creating the amp electronically and cosmetically in every detail as they were built in 1966. I will be going by there soon and playing through it a bit. He just bought a Freeman matching 2-12 cab with vintage 30's in it and he also has a 4-12 Marshall cab but not matching. Here is the link:
http://www.germinoamplification.com/#!monterey-100/c18r5

Thanks, Platefire

[Willabe]

Those Germino Marshall clones are said to be killer.

[Platefire]

Chassis prep continued:

finished drilling the cover plate for the PT wiring holes to chassis and tested inserting the grommets. Will now have to take them back out and finish the steel plate or it will rust pretty quick. IEC holes looks a little rough. Wasn't easy cutting it out around the existing hole with the tools I had on hand. Once the IEC socket is installed the roughness will be covered. Also cut another pot hole for the presence control.

Still need to drill mounting holes for choke and OT. Try to find some vinyl plugs to put in existing un-needed holes. After that the chassis should be fully prepped and ready for board/Electronics. Platefire

[Platefire]

Here is the Hot Shot 48 in it's former Glory done by Wooley in about 2002-2003 in that period when it was a Marshall 2203 circuit. According to him, the chassis came from Doug, he added the handles.

Edit: Also added a board picture of the original 2203 provided by Wooley. Hard act to follow!

[DummyLoad]

nice!


--pete

[Platefire]

Sometimes this stuff plays tricks on your mind

on this Classic Tone OT primary's  are blue/white/red

now I'm sure that the red is the B+ and blue and white to plates----just say Yeah!

For some reason white seems like a strange color to plates--just making sure. Transformer pdf dwg is attached. Platefire

[sluckey]

now I'm sure that the red is the B+ and blue and white to plates----just say Yeah!

WRONG! You better look at your wiring diagram.

[Platefire]

So you are saying center tap is B+ regardless of color(white).

Why they want to go messing with old standards?

[sluckey]

So you are saying center tap is B+ regardless of color(white).

yes

Who ever accused those Brits of having a sense of standards?   

[Platefire]

Thanks, Sluckey

Well I guess my OT Classic Tone is made in the USA but they had a color code comparison to the old Drake
OT I found in lower left hand corner of OT drawing as follows:

PRIMARY LEAD COLORS:

DRAKE    40-18025
WHT       BLU
BRN        WHT
RED        RED

every OT I ever installed to date(that I can remember), Red has been primary B+ but on the old Drake Brown was B+. So OK OT color code class is done for the day---glad I didn't hook that red up to B+

Platefire

[PRR]

> center tap is B+ regardless of color

CENTER tap. Push-pull. Think of a see-saw. If you move the pivot to the left end, and put the kids center and right end, it don't see-saw too good.

> Why they want to go messing with old standards?

There was no reason for the UK and US to have common standards until WWII. Not really a lot of cross-ocean mechanical or electrical trade. Different bolt threads. Different ways of specifying bolt tolerances. Different way of drawing blueprints! Some of this was cleared-up, enough to make guns and tanks. There was some feeling there should be more commonality. But UK cars and cycles used Whitworth bolts into the 1970s-- why change?

You know a US RETMA/ASA color code.

Apparently UK transformer makers knew another code.

There was little cross-Atlantic transformer trade until the Williamson, mid-1950s. Even then, the cost of shipping large iron over the water fostered many USA clones. Also a true Williamson, or the UL variant, has so many leads that the builder really has to Be Careful. UK color codes may have been rare in the US until the Marshalls started coming in large numbers.

If you are restoring a fine old UK Marshall, you "HAVE TO HAVE" the original genuine wire colors. ClassicTone does it correct per the originals.

> glad I didn't hook that red up to B+

Interestingly, it would not blow up. But it would be way-way down on power. Like the see-saw with the pivot at one end instead of center.

[Platefire]

Thanks PRR for the history on this. I guess we are a little more Globalized on standards now days. Since I've been working on this Marshall Clone, I have been reading up on Marshall history. When Marshall first started importing amps to the states they ran into issues on what power tubes to run in them. I think the one shipped to Canada had one type power tube and the USA had another and the ones in England another.

I still shy away from metric but use it when I haven't got a choice. I have to use an American vs Metric comparison chart. Platefire

[Platefire]

Yeaa! Finally got the old chassis fully prepped for all the holes with cover plates and plugs for existing un-needed holes. I had truly forgot how much work is in re-purposing an old chassis like this. But finding the old Hammond transformers and the Hoffman chassis is what got me started in the direction of a new/old project. So I looking forward to shifting gears and to start on the board and electronics.

One question???? I got my hole for my bias pot centered about 1 1/4" away from the center of my speaker output jack. Since I've never needed to put these two functions that close before, just wondering it there could be any conflict there? Platefire

[sluckey]

I got my hole for my bias pot centered about 1 1/4" away from the center of my speaker output jack.

That's OK.

[Platefire]

OK, Good! Thanks Sluckey

[Platefire]

Had quiet a break from this project. Ordered the 6-50uF/600 caps today and trying to re-remember where I left off. The chassis is pretty much prepped now(I think?), so I can start concentrating on the inners. Platefire

[Paul1453]

The bias circuit runs low negative voltage with very low current that doesn't fluctuate that much.

That circuit shouldn't be very susceptible to bleed over signals because of that. 

High voltage wires with big fluctuations of current and voltage are ones to give extra space to.
OT primary wires for example.

[Platefire]

I think next step may be drill the board and add turrets. I'm pretty mindful of giving high voltage DC their own space as much as possible. The only thing is I'm starting to second guess my circuit design with one of the channels preamp becoming a hot switch. I only wanted one input jack, so I'm supposing that is the best way to go. Just need to be sure I've selected the best 2204 channel for clean that will be normally on all the time because I'm mostly a clean player and the other best voiced for OD combination with the clean channel. Dummy Load seemed to approve of the design and very much assisted in the layout and board layout. So not being a Marshall specialist, I'm feeling my way!😉Platefire

[Ed_Chambley]

So you are saying center tap is B+ regardless of color(white).

Why they want to go messing with old standards?

Plate, the colours are different with Drake OT's and Heybour's copies of the Drake Transformers.  Since the size of the 50 Watt version they made is so close to the 100 watt, that is the only way I can tell them apart without figuring the winding ratio.

[Platefire]

Been a long time since I looked at my ClassicTone OT. In Gulf Shores Alabama right now for two of my Grandaughters Summer Camp Cheer Leader Competition-----push it----push it---know what I mean? Platefire
 

[Platefire]

Back Home now. Referring to Ed's post #193, I think this has been discussed previously on this post but here is the OT I got for this project. As shown primary ct is white and plate leads are blue and red. In the lower left hand corner of drawing it does have a primary lead color code comparison of Drake to ClassicTone, the Drake ct was brown as compared to CT white ct. Platefire

[Platefire]

Got my 50/600V filter caps and my 25K L locking bias pot in. I think that's it on parts---I just need to go to work. Where did i put that drill press?

[Platefire]

DummyLoad, I sent you a PM regarding last board layout you provided. Trying to get started back on the right foot! Platefire

[sluckey]

Dummyload has not been on the forum since May 11. Hope he's OK?

[Platefire]

That sounds very unusual for him, I hope he's OK too. Platefire