PT/OT distance?

[Madison]

How close can they be positioned to each other at right angles?

I have come within a few inches of each other before with no problems but I want to even get tighter.....like 2 inches or less.

[sluckey]

I've seen them less than an inch apart. And as far apart as possible. And just about anywhere in between.

[kagliostro]

Only note that the two transformers that are near (first photo) have an iron shield

Kagliostro

[Willabe]

Again heat could also be a problem.     


                   Brad       

[tdvt]

Not to hijack, but does anyone know if this type of transformer cover is readily available anywhere?

And wouldn't they help with noise as well?

[sluckey]

You can get that style over at fliptops.com. Kinda pricey though.

[cbass]

Trainwrecks have the PT and OT very close together and they are fairly high gain amps.

[Madison]

Trainwrecks have the PT and OT very close together and they are fairly high gain amps.

That's right.
I totally forgot about that.

[jojokeo]

Besides causing the weight balance to be off, I don't do this anymore. I can show you many amplifiers with the PT & OT on complete opposite sides of the chassis. As for Fender amps, many PT's are the laid down type. This makes a big difference compared to stand-up types. Make yourself a quick and easy "listening" amplifier and you can hear the results and differences as to placements to each other before you mount the trannies.

[Tone Junkie]

The headphone trick is real good for telling how much noise there is when there close. Now I just have to find the thread.
Thanks Bill

[12AX7]

Is noise the only potential issue or can it affect tone, and If so in what way?

[jojokeo]

Is noise the only potential issue or can it affect tone, and If so in what way?

I don't think it's affects tone but your tone is screwed up if you hear more buzz/humm than you otherwise would. I have seens issues when the trannies are really close and you're using close to full power - really sounds nasty and unusable in those cases. This is what I attribute it too anyway. Very high currents going in this condition. I build mostly scratch amps drilling my own chassis' so for me this is an important issue - just like grounding in concerned. For those buying already pre-fabbed chassis' there isn't really a choice most of the time. There's many sayings for things like this such as "an ounce of prevention is worth a pound of cure".

[Madison]

Besides causing the weight balance to be off, I don't do this anymore. I can show you many amplifiers with the PT & OT on complete opposite sides of the chassis. As for Fender amps, many PT's are the laid down type. This makes a big difference compared to stand-up types. Make yourself a quick and easy "listening" amplifier and you can hear the results and differences as to placements to each other before you mount the trannies.

I am going to do this!
I have done the headphone trick but not for a long time.

I scratch build most of my original designs now days.

My idea did not work out; tubes up front, near the pots was a terrible experience.Hummed like mad.

I will try again with pots in front and tubes in rear.
The chassis I am using is only 6" X 12" with 50 watts running inside.
It may still be tough to pull off?

[jojokeo]

Found a previous thread discussing my tranny placement results (& types) along w/ manufacturers putting their trannies on opposite ends of the chassis.

http://www.el34world.com/Forum/index.php?topic=10378.msg95443#msg95443

[John]

My idea did not work out; tubes up front, near the pots was a terrible experience.Hummed like mad.

Thanks for mentioning that! I haven't started drilling holes yet.

[Shrapnel]

I scratch build most of my original designs now days.

My idea did not work out; tubes up front, near the pots was a terrible experience.Hummed like mad.

I will try again with pots in front and tubes in rear.
The chassis I am using is only 6" X 12" with 50 watts running inside.
It may still be tough to pull off?

The idea: tubes up front. Was that on the same size chassis you refer to, 6" x 12"? Do you think the size of the chassis could have an effect?

[jojokeo]

"Do you think the size of the chassis could have an effect?"

It depends on how sophisticated of an amp you're trying to build w/ how many tubes and how much circuitry it's going to require stuffing it all in closely together. Lead dress will have few options, sensitive wires will not have spacing or crossing at right angles, hard to keep the circuit flow from crossing over itself, and heater wiring will be suspect and close to these things also. It's not that it can't be done, but it takes good planning w/ special care on your layout.

[Madison]

This what I ended up with.It's now taken apart.
This pic was when I started trying to put a bunch of shielded wire, unsuccessfully.
It's a B-15 copy which isn't very high gain.
Waiting for another chassis to arrive.

[jojokeo]

It looks great Madison - to the untrained eye. Heater wires near the input and then those sensitive preamp wires/pots and then the output tranny wires also near them (all the white wires) is what did things in most likely.

[Madison]

It looks great Madison - to the untrained eye. Heater wires near the input and then those sensitive preamp wires/pots and then the output tranny wires also near them (all the white wires) is what did things in most likely.

Thanks.
I kind of thought the same thing about the heater wiring plus the wiring to the pots were just too manic.
Going to flip everything around the "right way".
I hope that will fix it.

[Shrapnel]

I asked about size, because I know without the right layout, AND if it's crowded, it could possibly add up to it.

I've got pics of what is basically a Marshall "master-volume" preamp on a EL84 output (practically original topology for the PA of the Davis 201-A it was, AND in the same case) point-to-point and it's pretty quiet. (Notice how close the heaters are to the shielded input of the first preamp tube in the third photo) This is a front-to-back arrangement though and not side-to-side. (No g2 resistors at this time. Just copied the original PA, and I haven't really cranked it. I'll eventually get around to adding them.) I think the knobs are 1.25" diameter IIRC.

[12AX7]

Has anyone considered how much the wires and caps contribute? I started putting the filter can (multi) on the very far side with the PC and routing all the wires to the nodes outside the amp (teflon jackets) bundled in heat shrink and each wire leaving the bundle and going thru the chassis right below it's destination. Same with the OT. Mine hummed loudly till i did that and now theres none. (assuming the quiet due to wire/filter placement more than OT wire changes) And the PT and OT have always been close since i initially built it, the choke is between them, but thats only 3-4". I used the headphone trick to locate.  I DO have some buzz, but it's not hum at all, sounds like single coil buzz. Not sure that could be from tranny placement.

[Willabe]

It is my understanding that Multi cap cans tend to have more hum problems.

There is good info in here on why multi cap cans can cause problems. Also a lot of other good reading.

http://www.freewebs.com/valvewizard2/Grounding.html


                           Brad     

[Madison]

I haven't really had an issue with cap B+ routing.

Anyways, back to PT/OT.

I did some experimenting with a few different PTs and OTs I have.

I think all the examples people have shown on this thread are 15-18 watt amps.
I am working with a 6x12" chassis.Those outputs would work in there.
50 watts just doesn't want to live happy in there with the headphone trick, no matter where they were positioned.
A set of 5E3 type PTs/OTs were okay, barely.
Of course a 5F1 set up was no prob.

So, I will have to put this 50 watt project in a larger chassis.(14X8 is what I have used many times in the past for this output)

Nothing scientific here and YMMV.
Peace.

[darryl]

The headphone trick is useful for determining transformer placement so induced hum can be minimised, but it is unrealistic to expect no hum with such a sensitive test. Once you have found a practical transformer layout where hum is minimal, connect a speaker instead of headphones and see if the hum level is objectionable.

Different transformers will have varying susceptibility to hum induction, but a fifty watt amplifier should still be practical on a 6 x 12" chassis.

This is a 45 watt amplifier built on a Hammond 1550J aluminium box, with no hum issues. The chassis is 6.7 x 10.8". It has two power transformers, one for the B+ supply and one for the heaters.

[Madison]

What's the specs that OT?
It appears to be much smaller, in physical size at least, than what I am using.
But, yours may in fact be higher quality.

As I did my tests; the smaller the OT, the quieter things got.

I'll try your suggestion.Thanks,
Though I have already drilled out a bigger chassis today

Man, I wish I could do point to point.(I'm not ready for that, probably never will be)
Beautiful work!

[darryl]

What's the specs that OT?

It's an OT42PP transformer from Musical Power Supplies.

Quoting from their description:

Push Pull Output Xfmr 45W

4200 Ohm Inputs : 2,4,8,16 Ohm Outputs

Can also use as 8400 Ohm Inputs :4,8,16,32 ohms

[Madison]

Ah, I see.
Yeah, that OT is  much smaller physically (like half the size and weight) of what I been using use in 50 watt amps.
http://www.edcorusa.com/p/439/cxpp50-ms-6_6k

In fact, possibly smaller than 25 watt model OTs I use.
I can see how you could make that one work in those chassis dimensions.

[supro66]

Besides causing the weight balance to be off, I don't do this anymore. I can show you many amplifiers with the PT & OT on complete opposite sides of the chassis.

I agree

I have seen amps with their handle placed of center
so you can carry it at it's center of gravity

[jojokeo]

Darry, love the workmanship there and the extra time it took to make everything North to South and East to West on your runs and bends. I noticed a few goodies like the mustard cap near your input, the polystyrene caps, etc. Me likely. On your output jacks, I can't see the ground wire running from the jacks unless you're using a stealthy bare piece of hook-up wire that I think I can see?

*curious how/what the bright and dark vol controls are?
*I bet running separate PT's for heaters & B+ is helping you as far as noise in concerned?

[darryl]

I noticed a few goodies like the mustard cap near your input, the polystyrene caps. On your output jacks, I can't see the ground wire running from the jacks unless you're using a stealthy bare piece of hook-up wire that I think I can see?

*curious how/what the bright and dark vol controls are?
*I bet running separate PT's for heaters & B+ is helping you as far as noise in concerned?

The mustard capacitor and the couple of "styroseal" capacitors are from a very large quantity of components I purchased about 35 years ago, when much of the domestic Australian electronics manufacturing industry closed down due to the abolition of import tariffs. Unfortunately most of the capacitors ( and resistors ) I have are not suitable for guitar amplifiers. If I had hundreds of .022mfd mustard capacitors, rather than the .22mfd ones, I could almost have funded my retirement. 

There is a ground on the output jacks - it's a black wire running from the ground lug beneath the 47mfd electrolytic capacitor to the mid point of the hookup wire which is common to both output sockets.

This particular amplifier is very loosely based on a Fender 5F6-A, but rather than having separate input sockets for the two channels, there is just one socket providing signal to both channels. The outputs of these two channels are then mixed using the "bright" and "dark" volume controls.

I haven't looked into the noise performance of using two power transformers. In Australia, "real" power transformers for valve amplifiers are very expensive ( limited market, high freight costs etc... ) so low voltage off-the-shelf transformers are pressed into service. The B+ transformer has a 70VAC secondary, so the power supply uses a voltage quadrupler to attain the nominal 390VDC B+.

This particular amplifier build is being fully detailed at Australian Guitar Gearheads forum: http://www.guitargear.net.au/discussion/index.php?topic=32065.0  The pictures posted here actually pre-empt that build description.