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

[Platefire]

My satellite internet system is running so slow way back here in the sticks that the pictures to your dropbox won't open, so I'll guess I'll view them later!

Thanks for doing that experiment and doing the schematic. I'd say that is a good pre-view of how my amp will behave with the bias set up like that, two PP EL34's and two GZ34 rectifiers. I have no problem running the two GZ34's but it's going to be hard to live without a standby switch I think this is a conspiracy between you and sluckey

Hay, the two extra octal socket holes are there already, why not use them. Wow, I think that pretty much lays out the power section. I checked on the Classictone #40-18025 3.6K OT and they are on back order. They say it will be a week or two. Thanks a bunch  Platefire

BTW-Think I will take your experiment schematic and draw a proposed preamp

[Platefire]

OK, here is the schematic of what I think I want to build. I adapted DL's schematic and married it up with 2204 schematic with Doug's hot switch without relay. I know I've got stuff wrong, but not sure what. Please check me and let me know what's messed up. The Marshall schematic had filter caps prior to the choke and in DL's model only after? so I wasn't sure so I threw some in like the 2204 schematic?? don't know if that's needed?

I changed the V1a & b cathode resistors and caps like Doug's hot switch because he said it was voiced to not have too strong of a bass or treble effect on the signal. That sounds good to me however I haven't had much experience playing over Marshall value pre's. So this is what I envisioned making out of it---rather what I got will sound good and work right, I don't know? Platefire

[DummyLoad]

1) BIG error! - you have a capacitor loaded PT. the 50uF/50uF caps are connected AFTER the choke.

2) there is no junction at 100K NFB resistor & .022uF PI coupling cap. the 100K NFB resistor connects to the 10K tail & presence pot.

3) LTPI non-invering AC ground cap should be .1uF not .022uF

--pete

[Platefire]

Thanks pete! I think I've got it corrected, please check me out. I have grid resistors shown prior to the power tubes but didn't put a value on them because I could not find an example of that on any of the 50 watt Marshalls. On a 100 watter it looks like they had 5.6K if I was reading it right?

Also, should the NFB be connected to the 4 Ohm tap even though I'll be using the 8 Ohm tap?

Appreciate you help, Platefire

[Willabe]

Plate you moved the the caps after the choke that's right, but what's going to filter the A node B+?

[Platefire]

Willabe

If you go  back and read DL's last response, be said the PT is capacitor loaded. So I'm not familiar that and didn't know until he told me.

[Willabe]

Plate in your newest drawing there in no filter cap or choke filtering the B+ A node. You have to have 1 or the other.

[Willabe]

Look at the drawings in DL's reply #49.

[Platefire]

OK, Willabe--let's try this again and see if I'm getting closer to home

[DummyLoad]

this should work... please pardon, i cleaned up the draft a bit and rebuilt the B+ filter string.


respectfully,


--pete

[Platefire]

Wow! So we're pretty much there! Yea! That was a sweet clean up job DL on the Sch, thanks! As fast as you move with these schematics I can tell you have become pretty skilled using the PCB/Sch program---I'm still pretty slow with it. Thanks so much for helping me get this plan together and now I have something solid to go forward with for the build process. So let me see now, hmmmm parts---layout--->>>>>>>

[DummyLoad]

we forgot the grid stoppers for the EL34s. the EL34 symbols had the wrong pin-outs and the G3 connections to the cathodes were missing (pin 8 to pin 1). more clean-up and i added reference designations to all the parts, (e.g. R1,C1, etc..) to facilitate troubleshooting, if needed. lastly, i created a BOM from the schematic - another good reason to add reference designations to the components.

please review the attached revisions & BOM.

--pete


EDIT: uploaded corrected schematic and BOM. 

[Platefire]

Hay Man, that looks great! I was wondering about the grid stoppers but didn't know what value to put in there. The older Marshall schematics didn't have any. So the schematic and BOM is top notch and I didn't see anything that needed fixing,  thanks!

I determined last night that I wouldn't be able to re-use that old project board for this project. so I've been working on a new board layout using ExpressPCB. I've had that on my computer but never used it. I've only used ExpressSch for schematics, not boards. So I'm drawing it to scale so I can determine how much board material and turrets I will need, plus having a board plan for drilling.

I think in the area of the PT, I'm going to need to mount the PT and run wiring to the rectifier sockets, fuse, power switch and power cord to determine what kind of room is left in that area to install my filter caps/power nodes and bias circuit. Platefire

Edit: I do have a question on the schematic. I noticed you change the bright cap value on the tone stack treble cap from .0005 to .022? The values that were on there was from the attached 2204 schematic. Just wondering why you changed that?

[DummyLoad]

so sorry that should be a .0005 cap. cut and paste error. I'll fix it shortly.

--pete




EDIT: fixed and resubmitted please download new .sch and .pdf in reply 61. i'll fix the BOM and upload i a bit.

[Platefire]

OK, Thanks! Got the new versions.

[Platefire]

Any reason a bias circuit can't be adjacent to filter caps/power nodes? To be more specific AC feed from PT secondary to bias circuit 220K dropping resistor within about 5/8" away from "E" power node cap & resistor turret. Platefire

[DummyLoad]

Any reason a bias circuit can't be adjacent to filter caps/power nodes? To be more specific AC feed from PT secondary to bias circuit 220K dropping resistor within about 5/8" away from "E" power node cap & resistor turret. Platefire

that should be ok, just keep the filtered output connection(s) to bias tubes ckt. away from AC, HV or filament. 


--pete

[Platefire]

OK, Thanks. Happy New Year!

[DummyLoad]

>>> Happy New Year!


back at ya! ...and good luck with this endeavor.

--pete

[Platefire]

Thanks! When I get my board/layout plan done, I'll post it for public ridicule

It helps IMHO being able to draw it to actual scale you can actually tell
How much space your taking. The only problem is I can't print it out full scale so I can use it for a drilling template. When I was working I had access to better tools to accomplish this type of thing--especially when it comes to high end CAD programs and large printers. You have to realy get inventive with the ExpressPCB to do everything needed. Still I'm thankful of what I do have. Thank you Jesus for another year! Platefire

[Platefire]

Got a question in the back of my mind I need to settle about this project. Haven't had any experience with EL34's but always thought of them as a high plate voltage operator. When I discovered my plate voltage with a load on EL34 would be around 380VDC, I was thinking that's kind of low, more in the range of a 6V6 but I thought, on the other hand it may be OK.

Last night I downloaded a EL34 spec sheet and one of the first thing I noticed was a 800VDC max.
This one is not going to be even half of that. So my concerns is will 380VDC be enough to tickle that EL34 to wake it up a bit?  Just wondering about that before I start ordering parts. Platefire

[DummyLoad]

Got a question in the back of my mind I need to settle about this project. Haven't had any experience with EL34's but always thought of them as a high plate voltage operator. When I discovered my plate voltage with a load on EL34 would be around 380VDC, I was thinking that's kind of low, more in the range of a 6V6 but I thought, on the other hand it may be OK.

Last night I downloaded a EL34 spec sheet and one of the first thing I noticed was a 800VDC max.
This one is not going to be even half of that. So my concerns is will 380VDC be enough to tickle that EL34 to wake it up a bit?  Just wondering about that before I start ordering parts. Platefire

plate, a pair of EL34 will make 48 watts with 375V. refer to the mullard or phillips data sheets. you can run them at 600V+, however, they are unreliable at those voltages. a simple mis-matching of load can cause arcing between elements (pin2-3 arc is the most prevalent) or even a poorly implemented standby switch can also cause arcing with high B+ amps.

http://tubedata.milbert.com/sheets/129/e/EL34.pdf

yes, you could run a quartet of 6V6 for about 40 watts, but why?

things that we build with larger pentodes are best kept at or under 500V B+.

--pete

[Platefire]

OK, I see--Pentode, fixed bias, push pull=375 to 400VDC. I figured it was just my lack of knowledge
but at the same time I had to ask the question so I could get the little nagging questing out of the back of my brain. Thanks, that clears that up--have no desire to run anything other tube than what we planned for. Still working hard on the layout plan. Thanks, Platefire

[shooter]

my plate voltage with a load on EL34 would be around 380VDC

My last build *copied* the matchless clubman PA section, B+ about same as you(380vdc).
It's self biased, so I'm around 25W into a 2X12, fixed bias should get you more.
Mine is LOUD! and sounds very nice, I started with 88's but liked the 34's sound better.
fwiw

[PRR]

> a 800VDC max.

As said.... that's frickin' dangerous.

Philips was anxious to improve sales. Most other octal tube makers thought 800V on the Octal base was "very aggressive rating".

At 775V you "can" get 100 Watts per pair. There was a professional amplifier working at this level. It was part of an even larger amplifier(!) so the need for strict regulation and load-control was absorbed in overall general expense. But EL34 is also a low-price tube, and you have to wonder if four bottles at 400V might have been a safer design.

Obviously Marshall et al felt that 4 jugs for 100 Watts was a fine design.

The EL34 is perhaps more able to suck hard at low plate and screen voltages than the older tubes like 6L6.

> 48 watts with 375V

Or at lower load, 44W with 350V.

11 Watts SE with just 250V plate and screen (265V supply).

[Platefire]

Sorry to cause so much ruckus!  I'm very well satisfied that the EL34 will be fine in this amp.
This will be my first EL34 amp, so learning a lot of stuff.

Something else I just learned is making any drawing in ExpressPCB is a waste of time because the forum don't support that PCB file format. So I discovered I can't do nothing with my layout drawing
in converting it to another file that is compatible with anything. The only thing I found I could do is print it out and scan it. So attached is the scan of the layout.

Please understand I am trying to make this thing work in an existing chassis that already has many holes. So that's one reason it's laid out the way it is. Also I wanted to draw it to scale so I could see how everything would fit and connections would hook up. So unless I made some awful mistakes, from what I'm seeing in my layout, I think it will work. If you don't think so, let me know. Platefire

[DummyLoad]

Sorry to cause so much ruckus!  I'm very well satisfied that the EL34 will be fine in this amp.
This will be my first EL34 amp, so learning a lot of stuff.

Something else I just learned is making any drawing in ExpressPCB is a waste of time because the forum don't support that PCB file format. So I discovered I can't do nothing with my layout drawing
in converting it to another file that is compatible with anything. The only thing I found I could do is print it out and scan it. So attached is the scan of the layout.

Please understand I am trying to make this thing work in an existing chassis that already has many holes. So that's one reason it's laid out the way it is. Also I wanted to draw it to scale so I could see how everything would fit and connections would hook up. So unless I made some awful mistakes, from what I'm seeing in my layout, I think it will work. If you don't think so, let me know. Platefire

wiring errors that stand out
- on V2, move the jumper on V2 from: pin 2 to pin 7 to: pin 1 to pin 7.
- on neg bias PS: 33K/25K pot going to 220K grid-leaks - 33K should be tied to bottom of bias pot, other end to ground - top of pot & wiper goes to 220K grid-leaks - that was my error, not yours. sorry!   
   
i updated schematics, please see attached. 

- one typo - 320K plate for V2 should be 330K 

--pete


EDIT: if it makes things easier for you, swap locations of 33K and 25K pot. so then bias supply to grid-leaks would be from node of 10K & 22uF & 33K to the two 220K resistors. 

[Platefire]

Thanks! I'm still a little confused about the bias pot hookup. Check my new revised scan to see if that works? Platefire

[sluckey]

That works. May I suggest... rather than running two wires to the bias pot, just run one wire. The second wire can be a short jumper on the board.

[DummyLoad]

no, not ready quite yet, the error on V2 is still there. please re-read schematic: connection is from V2a plate (pin1) to V2b grid (pin 7). so jumper is from pin 1 to pin 7. layout still shows pin 2 to pin 7.

other error is on V3 now:

you moved jumper on V3 - V3 jumper is pin 3 to pin 8 ( cathodes bonded).

respectfully,


--pete

[DummyLoad]

marked up layout attached.


--pete

[sluckey]

May I suggest this layout for V2. Put the 330K directly on the socket. This layout is very common and in your case will save 4 turrets on the board.

[Platefire]

Yes, thanks sluckey and while we are talking about board space--the two caps 22 caps at 160V in the bias supply are almost non-existent in my searches so far. There are 22's at lot higher voltage that are also larger caps from .64" x 1.25" to .80" x 1.625".

So as you see on my board I just used symbols and didn't account for a large cap. So what I am saying is if I can't find a smaller cap to fit in a space a 100/100 would fit in, I will also need to open up the board in that area to make room. So you may of just bought me that space. Platefire 

[Platefire]

Wow you guys keep accumulating more mistakes on this layout! Where in the world are they coming from

Less Smoke, no Joke!    Thanks for Looking!

[DummyLoad]

Yes, thanks sluckey and while we are talking about board space--the two caps 22 caps at 160V in the bias supply are almost non-existent...

http://www.mouser.com/ProductDetail/Nichicon/TVX2C220MCD/?qs=7EEPR5pZqDfnCUD2VG1N7g%3d%3d


http://www.newark.com/vishay-bc-components/mal204121229e3/aluminium-electrolytic-capacitor/dp/98K6692


http://www.ebay.com/itm/like/331731305014?ul_noapp=true&chn=ps&lpid=82

[sluckey]

the two caps 22 caps at 160V in the bias supply are almost non-existent in my searches so far.

Why even use 22µF caps? Marshall was very fond of 10µF bias caps. Doug has 10µF @ 100V that are only .25" diameter and .5" long. I'd use those if I had to buy some.

[Platefire]

Did I say "non-existent"?  It must be a good reason DL is liking the 22/160. The 10/100 would certainly fit better in the slot. Thanks, Platefire

BTW-A fellow would have a hard time finding excuses why he couldn't do something around here


A big ol THANKS

[sluckey]

must be a good reason DL is liking the 22/160

Probably for the same reason I use 25µF @ 150V. Bet he has a bin full of 'em.   

     http://sluckeyamps.com/6v6plexi/P-6V6_05_big.jpg

A fellow would have a hard time finding excuses why he couldn't do something around here

'cept when it comes to standby switches! 

[DummyLoad]

platefire: MAKE SURE you use the correct black wire on the primary. if you mistakenly use the 110V black and 120V brown you WILL FRY the PT.


the correct black and brown taps will have  approx. 5 to 6 ohms resistance.


--pete
 

[mresistor]

You could save more space and one turret if you put three turrets in a row and mounted the diode and 220K of the bias circuit like you did the input components to the EL34 grids.

[DummyLoad]

mresistor's suggestion depicted. 


--pete

[Platefire]

Yes, thanks! Good idea. But DL, what did you use to manipulate my scan? Platefire

[DummyLoad]

Yes, thanks! Good idea. But DL, what did you use to manipulate my scan? Platefire

M$ paint...   


--pete

[PRR]

> caps 22 caps at 160V in the bias supply are almost non-existent

When we all fixed ACDC table-radios all day long we bought a lot of 150-160V caps. 117V*1.414 is 165V, but rectifiers sucked, profit was tight, and 150V caps were common.

This is a lower-Voltage EL34? Then you don't need even 40V on the grids. With trim, you might want 75V caps.

But 160V for bias-supply on non-insane amplifiers suggests a big pile of leftover table-radio caps which need to be cleared-out. Gar used them like they were going out of style (which was exactly the situation).

[Platefire]

platefire: MAKE SURE you use the correct black wire on the primary. if you mistakenly use the 110V black and 120V brown you WILL FRY the PT.


the correct black and brown taps will have  approx. 5 to 6 ohms resistance.


--pete

DL, I taped the two primaries that were connected/used together so I'd be sure re-use the same ones. The Ohm reading you suggested don't match mine? Reading Ohms in between the Primaries mine looks like this:

Black & Brown that was used=1.8 Ohms

Black (un-used) & Black (used)=1.6 Ohms

Black (un-used) & Brown (used)=.5 Ohms

My meter has .3 Ohms just touching the probes together.

So why is mine reading below what you said it should be??? Platefire

[DummyLoad]

platefire: MAKE SURE you use the correct black wire on the primary. if you mistakenly use the 110V black and 120V brown you WILL FRY the PT.


the correct black and brown taps will have  approx. 5 to 6 ohms resistance.


--pete

DL, I taped the two primaries that were connected/used together so I'd be sure re-use the same ones. The Ohm reading you suggested don't match mine? Reading Ohms in between the Primaries mine looks like this:

Black & Brown that was used=1.8 Ohms

Black (un-used) & Black (used)=1.6 Ohms

Black (un-used) & Brown (used)=.5 Ohms

My meter has .3 Ohms just touching the probes together.

So why is mine reading below what you said it should be??? Platefire

cool! just concerned.


my mistake, i measure 1.6 ohms on the 120V winding on the PT i have.


--pete

[Platefire]

OK, goood! Ready to Roll>>>>>>>>>>

Thanks for letting me know the danger of smoking a PT, I'll be super careful. Platefire

[mresistor]

mresistor's suggestion depicted. 
--pete

Hey DL  that was way cool, I wish I had half the talent you and some others here have with the software.  If the caps are small enough  one could delete two more turrets on the 22 uf caps to the east the bias diode. one could delete the middle turrets, and fit the caps to the real estatate.   :-)

[Platefire]

I re-arranged my board layout drawing to include most of your suggestions. The length of the board has been reduced from 13" to 12". I could of reduced it another 1/2" probably but didn't see the need. 12 is a good round  number.

DL, on the my layout scan you manipulated to change the bias dropping resistor and diode---haven't you got the diode facing the wrong way?

I called myself checking everything to see if I got everything connected back up right, but you know how that goes! I welcome you to check me out Platefire

[DummyLoad]

100uF? for bias supply filters? seems like overkill but at least the hum source won't be the bias supply!      


22uF is borderline excessive, 47uF is probably prodigal.


--pete