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

[sluckey]

What's your question. Maybe someone else can answer. I've got the latest layout revision but I don't know which schematic is your final version. Can you point to the correct schematic?

[Platefire]

I've been reading old post trying to get up to speed. In the last of Jan 2016 we were decided we could go from tube rectification to diode if we went to 600V caps. So we did that but that didn't get revised on the schematic. Attached is the most update schematic I have still using two 5U4 rectifiers. I need to fix that.

At about that time DummyLoad started working on the board layout plan to make it more efficent. He started using his own drawing program to produce these layouts. So if you follow the post he went through several revisions of the board layout until the last on post #155 23 Jan 16. The pdf file of that is attached.

My questions were this:

1-It appears to be a obvious mistake on his last layout on the B+ to the first filter cap shown "To diode board" should be from "From Choke". The choke would be between diode board and first filter cap.

2-In the earlier versions of his board layout drawing specifically at post #147 20 Jan 16, he had a the ground wire going under board with dotted lines to the preamp section of the board but on the post #155 latest version he went back above board with most of the ground----------so I was just wondering about his reasoning for doing that? I kind of liked it below board where all those signal wires cross.

3-Last but not least----in sizing up my drilled board with the existing Hammond Choke I found the red lead to board is about 1" short to reach the first filter cap turret. My plan was to install another turret on the board that the red lead will reach and attached it to that and run good heavy wire from choke turret to filter cap turret to make up the difference. It's either that or extend the choke lead with a soldered in/shrink wrap wire extension. Which way is best?

That's about it. Getting ready to install my turrets on the board and just need to drill any extra turret holes if need be first!
Again I hope DummyLoad is OK, got me wondering? Platefire

[sluckey]

1. Yes, it's a mistake. But you know that so it's not an issue, right?

2. Only Pete knows his reasoning. I would put all the ground jumpers on top.

3. Either way works equally well. I'd just make the wire longer. Don't you have a small wire stretcher?

[Platefire]

Regarding #3--Is a small wire stretcher like going Snipe hunting and sky hooks?

[TIMBO]

Hi Plate,
Skyhooks are a real thing, we have them in Australia.
https://www.youtube.com/watch?v=5nvth-kGtQ8
https://www.youtube.com/watch?v=3eqmW8lqiEc

[PRR]

> Skyhooks are a real thing, we have them in Australia.

Skyhooks' "Ego..." was a big hit in my crowd. Still have the 33-1/3 vinyl. Rather let-down to discover it never charted in the US.

I have a large wire-stretcher; rather a rope-stretcher, a half-ton comealong. Makes nylon rope considerable longer than you'd think. Probably over-kill for chassis wiring.

[Platefire]

Never heard of the Skyhooks until now. At least if I get sent to get a skyhook, I'll know what to look for now! Still looking for them small wire stretchers!

[PRR]

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

Look in Pete's "Dummyload" profile, there is a web-site. At that site there are email contacts for Richard and Pete. I got a response back in hours; he's "doing well" but has not had time for the forum.

[Platefire]

Good and Thanks for checking PRR, Glad he's OK. He went the extra mile in helping me with this amp, so I'm very appreciative. I need to reciprocate and finish the job. Platefire

[Paul1453]

He has given me excellent guidance and specific modifications for a Bogen K10 PA. 

I too am glad to hear he is well.

Most of us tube type guys are getting up there in age.
Any of us could be here today, and just gone tomorrow.   

I'm thinking that most of the amps I'm making will easily outlive me now. 
Since I'm not a great musician, I consider these as sort of my musical legacy.
I'm hoping that 50 years from now, some kid will still be rocking out with one of my amps.   

[Platefire]

Well back to the Hot Shot 48. Little progress---got power supply board and main board drilled, chassis drilled for standoffs and a test mounting to see how it fits and looks. Next installing turrets. Not much but something!!! Looks pretty rough don't it!  Platefire

[Platefire]

Got s question? Please look at attached PDF and see view of main board with components.The bias voltage circuit output goes under board to the 220K bias resistors. It crosses path with the under board B+ to PI. I usually try to avoid these kind of intersections but in this case seems unavoidable. Is my concern unwarranted or is there a way to route around I haven't seen? Platefire

[sluckey]

No problem with those wires crossing. But your bias diode is backwards on the layout.

[Platefire]

OK, thanks sluckey! I want worry about that anymore and thanks for pointing out the wrong direction
On bias diode.  Dummyload produced the original, so I'll just mark it on my hard copy. Platefire

[Platefire]

I never revised my Schematic when I decided to change plan from tube rectifiers to diode. Attached is the update. If you see any problems, please let me know! Platefire

[Paul1453]

What voltage are you seeking for your B+?

It looks like you will be around +600V with what you have there.   

[Willabe]

Plates drawing shows the B+ as choke loaded as opposed to cap loaded, B+dcv will be lower.

[sluckey]

You have a PI wiring error. Make the changes on the attached pic.

Your B+ will be fine.

[PRR]

> Your B+ will be fine.

With 2.5 Henry, looks like anything under 120mA (cold bias, but also start-up, also stand-by) it will be rising toward 550V, thus threatening to electrolytic caps.

Hammond used a bottled rectifier (slow start), no standby, and also drew a lot of Field Coil current all the time, so they could be sure it stayed near the 0.9* choke-input range instead of the 1.4* peak-catching range.

Many Hammonds also used 600V oil caps just to be sure of no blow-up when tubes and speakers were yanked. If those oil caps are lost (or never fitted), then I'd be thinking 2*350V caps stacked.

[sluckey]

With 2.5 Henry, looks like anything under 120mA (cold bias, but also start-up, also stand-by) it will be rising toward 550V, thus threatening to electrolytic caps.

Had not considered that. The PR-40 uses PM speakers so there is no constant current drain on the power supply.

Why did you decide to abandon the dual 5U4s? I think I'd put them back.

[Paul1453]

>  the 0.9* choke-input range instead of the 1.4* peak-catching range.

I did notice the 1st E-cap was after the choke, instead of before as seems more common.

These type of design issues often escape my repair tech only trained eyes.  So I'm learning.
Thank you PRR!   

After thinking about it a little, am  right to conclude that in this configuration the choke limits the voltage to .9*

because it is resonating with the large amount of AC ripple still contained in the just rectified DCV?

Is this also used as a common technique to drop some voltage without creating a bunch of heat?   

[Platefire]

The reason I abandoned the 5U4's is Dummyload tested the same circuit I am building with the the Hammond PR-40 power supply with SSR. He said the voltage spiked up to 540 for a few seconds and then went down. Read reply #118 on page 3. I have 600V filter caps I am installing. I don't have to have the standby switch but I'm a church player and  have to get up and down to play for different parts of the service. When you do that, it's nice to have instant sound and instant mute. Platefire

Thanks sluckey for catching that wiring mistake on PI, revised sch is attached. 

[Willabe]

After thinking about it a little, am  right to conclude that in this configuration the choke limits the voltage to .9*

because it is resonating with the large amount of AC ripple still contained in the just rectified DCV?

Is this also used as a common technique to drop some voltage without creating a bunch of heat? 

Time to learn how to use the search feature here.   

You will find the info on other threads here, no need for a rehash.

[sluckey]

 

[Platefire]

So trying the glean something out of all the discussion, PRR I think? is saying if I use a standby switch I need a pre-standby cap arrangement like a twin with the two 100/350 caps/220K resistors? Would this help with what I'm trying to do? I think I may have room to add it if need be. Platefire

[sluckey]

PRR I think? is saying if I use a standby switch I need a pre-standby cap arrangement like a twin with the two 100/350 caps/220K resistors?

No, he's not saying that at all. His concern was for the voltage rating of the caps in your schematic as drawn. He did not know you were using 600V caps.

You cannot put any caps before the choke. The choke must remain the first thing your rectifier sees. If you put a cap before the choke, you no longer have a choke input filter. You will have a more common cap input filter and the unloaded B+ with that PT will soar to 440 x 1.414 = 622v!   

[Platefire]

OK, you got me a little cornfused(not hard to do) because I was using as a reference the attached twin sch that does have caps prior to the choke---or were you just referring to my specific situation in this case with the Hammond Choke. Platefire

[sluckey]

We covered all this back in December. Go back and read it again. That Fender PT only puts out 340VAC. Your PR-40 PT puts out 440VAC.

BTW, you should at least reconsider your rectifier choice. You have a unique opportunity to build one of the original "Dual Rectifier" amps. How cool is that?

[Platefire]

I may would have gone with the 5U4 rectifiers if you had got to me earlier but at this point it would require too much back tracking---so I'll go with the SS. Platefire

[Platefire]

Please have a look at this. I'm soldering connections on my board and got to looking at this bias circuit double checking things. Something don't look quiet right where the board drawing shows connection to bias pot term 1 & 2 as compared to what I have got on the schematic.

It seems to be a conflict the way the bias voltage is going through the bias pot prior to going to the 220K bias resistors on the schematic and then on the board drawing the bias pot is hooked up in conjunction to the 220K resistors?? It appears to me on the schematic, the bias pot has the jumper from term 3 to 2 instead of 1 to 2 as indicated on the board drawing. 

I know the bias diode on the board drawing is pointing the wrong way, so I have reversed that!

Also on the 33K resistor I am assuming since it is not on the board would be just connected to
the bias pot term 3 to ground.

I'm a little confused on this, please help. Sch and board drawing is attached. Thanks, Platefire   

[sluckey]

Schematic is wrong. Is this better?

[Platefire]

That is Better! Thanks for clearing that up for me sluckey    I did revise the schematic to reflect the change and also I rearranged the jumper on the bias pot so the connection would be to terminals 1 & 2 from the two 220K bias resistors intersection as to agree with Dummyloads board note. Revised Sch is attached. Platefire

[Platefire]

Getting close to where I can start wiring it up. Sowing up little small details like grounding points/lugs first. Platefire

[Platefire]

Fixing to get back on this, so I'm bumping it up to make it easier to find. Platefire

[Platefire]

Starting to wire things in. It's been a very busy summer that seems to be still going on.
So I just been hitting a lick here, a lick there as I can work it in. With 12 grandchildren, there
Is something always going on

[Willabe]

With 12 grandchildren, there Is something always going on

Time to start them younguns to work on building Grampa his amps. 

[Platefire]

  I could have some choice words regarding that, but I'll just keep my mouth shut

[Willabe]

To me or do you mean family? Sorry if I said something wrong Plate, I meant no disrespect to you or your family.

[Platefire]

Oh No, didn't take it that way. What I was thinking was, it would be more work to get my grandchildren to work than do it myself. There I said it. Don't get me started---the whole discipline thing has turned on it head since I was a kid but that's another subject for another thread. Platefire

[Willabe]

Oh No, didn't take it that way.

Good, just wanted to make sure. 

Don't get me started---the whole discipline thing has turned on it head since I was a kid but that's another subject for another thread.

    Yes it has and yes it is a whole another thread.

[Platefire]

I'm not that easy offended Willabe, you'll haft to try harder

I'm getting the old spare parts clone pretty much wired up. I try to wire up as much as possible
before I strap the transformers on then the chassis gets really hard to move around, those transformers are big bruisers.

Taken off on a little fall tour with my wife to celebrate our 50th anniversary. Going to head up to Branson, Mo. Then drop by Salem Ark. on the way back where my Grandparents on my mothers side lived. I had some great times there as a youngster. So the Hot Shot 48 completion will be delayed yet again. Of course there will most likely be tweaking after that(initial fire up) and then a wood head cab to house it in. Platefire 

[sluckey]

I'm sure I just read a reply this week stating you had completed this amp and had been playing it a while. Am I mistaken? If not, what happened? As much time as the forum has invested in this we need to see some pics and even hear some of that good gospel rock 'n blues.

[woolly]

I'm with you sluckey  ??

[Platefire]

I messed up, I was talking about the Snake Head Pro Reverb and accidentally posted it on this thread. When I realized it, I removed it and re-posted on the right one. Just let me have my senior moment guys!

[sluckey]

I had to ask because I thought I was having one of those moments too! If you read my posts you'll see I've had more than one recently. 

[frankenxtein]

I have a PR-40 Power supply .... well it will be here in a couple days. Went looking for something to build with it. This thread is very interesting , being just a novice I've been lurking here.   

[Platefire]

Well I finally got back on this thing today and installed the PT. After I got it installed, I decided I would run a voltage test to see if the voltages are good. So all I got hooked up is the power transformer wired up to the power switch, Fuse, pilot light, power supply diodes and the bias circuit---as shown in the attached pictures. The voltages readings are recorded on the Power supply drawing(sch below) drawn by Dummyload. My readings are contrasted with Dummyload's earlier readings on his PR-40 PS with larger text, highlighted and in parentheses. Please disregard the choke and filter caps, they were not connected on my amp yet--- Only the filter caps in the bias supply. Please check me out and see if everything looks OK. My DCV output from PS diodes is considerable higher but mine is unloaded and his might be loaded? Platefire

BTW-Frankenxtien----I should have this completed in a few days and will be posting the first test. Stay tuned! Planing on completing it over the holidays.

[sluckey]

That's fine if you don't intend to use the 4Ω tap.

My heart is beating faster with the excitement! Hurry up Plate! 

[Platefire]

Yeah Thanks, I deleted my question because I looked on my schematic and it shows two jacks, 8 Ohm and 4 Ohm sharing the common black with a switch  4 Ohm to ground when un-plugged on the 4 Ohm tap. I think I'll go ahead and do it that way since I've got it drawn that way. That would make the NFB hookup a little more normal:>)

Yeah I installed the Choke and OT tonight and doing miscellaneous wiring/soldering. My goal is to have it running before Christmas. Sooner the better. Platefire

[sluckey]

with a switch  4 Ohm to ground when un-plugged on the 4 Ohm tap

Don't connect anything to the switch lug on that 4Ω jack (J3). That will mess things up when you want to use the 8Ω jack.

EDIT... Oh, and your presence pot should be 22K, not 5K.