redplating 1959 w larmar

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Re: redplating 1959 w larmar

Post by flemingmras » Mon Feb 15, 2010 5:27 am

Roe wrote:could caps affect this as well? I'm using the sozo 4 100uf caps for screens and mains (for a total of 50uf on mains and 50uf on screens). PI caps is a F&T 32+32uf and preamp F&T 16+16. all caps have been slow-formed according to larry's method (a 100k after rectifier)
I would say no here. According to your filtering scheme, the TOTAL filtering is LESS THAN a later model Marshall. This means that since your amp has a little less filtering than a '68-'69 Marshall does with "theoretically" the same power transformer, that if the originals didn't replate yet yours is, this points to the fact that Metro's power transformer is obviously more efficient than the transformer that it was supposed to be a clone of in that it CAN keep the filter caps charged vs an ORIGINAL PT that would sag under filter cap recharge demand.

In other words...due to the efficiency of modern technology vs. the inefficiency of vintage technology, you're f**ked. :lol:
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Re: redplating 1959 w larmar

Post by martin manning » Mon Feb 15, 2010 7:25 am

raiken wrote:Since we can determine power using P=I^2*R, the power for one tube pair will be (500mA/1.414)^2*850 = 106W.
Just trying to keep up here... A 50W amp has 3400 Zpri, 1/4 of that or 850 for each side, and this is half of the duty cycle, so 106W here means (ideally) 53W average output power for the pair?

MPM

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Re: redplating 1959 w larmar

Post by novosibir » Mon Feb 15, 2010 8:29 am

No, can't see any reason for this!
It's rather the opposite with a 50+50 filtering, what's resulting in more sag than i.e. a stiffer filtering of i.e. 200+100

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Re: redplating 1959 w larmar

Post by raiken » Mon Feb 15, 2010 12:01 pm

I think we may be getting to the real problem, finally... If original Marshalls are designed to sag 100V at full load (that's terrible regulation!), they wouldn't follow the original loadline/curves for a 480V amp, the curves would shift way down to the equivalent of a 380V screen amp running a 3.4K loadline, which would greatly reduce the signal swing/power dissipation/output.

Roe: what is your test equipment setup, here?

Do you have access to a signal generator, or are you just hitting a guitar chord and measuring the sagged voltage?

Do you have a scope to look at waveforms, or are you just measuring voltages with a multimeter?

Do you have a resistive dummy load, or are you running into a speaker when testing?

RA

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Re: redplating 1959 w larmar

Post by raiken » Mon Feb 15, 2010 12:09 pm

martin manning wrote:
raiken wrote:Since we can determine power using P=I^2*R, the power for one tube pair will be (500mA/1.414)^2*850 = 106W.
Just trying to keep up here... A 50W amp has 3400 Zpri, 1/4 of that or 850 for each side, and this is half of the duty cycle, so 106W here means (ideally) 53W average output power for the pair?

MPM
No, it actually means 53W each, 106W total peak power, but that doesn't happen in real life because of output transformer efficiency, voltage sag, tubes not being the same as the "ideal" curves. You can get 100W out of a pair of EL34s, but you usually have to go higher in plate voltage and load resistance to get there.

A good example is what we are discussing right here - the loadline for a 480V Marshall says it should be putting out 200W, but the sag from 480V to 380V on a "real" plexi keeps it from actually getting there, so it only does around 100W. If you make the power supply stiffer, which is what is apparently happening with Roe's amp (although we are still trying to get to the bottom of that), it will put out more power.

Basically, you have to draw the loadline at the sagged voltage to see what is really going on. That's what we are trying to determine now, at this point in the thread - what is the real supply voltage regulation, i.e., how much sag are we really getting, and what is the real dissipation? Obviously, his amp is exceeding it for some reason, so we're trying to figure out why.

RA

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Re: redplating 1959 w larmar

Post by VelvetGeorge » Mon Feb 15, 2010 12:16 pm

The sag on our PT's is less, around half of that total drop under full output.

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Re: redplating 1959 w larmar

Post by Roe » Mon Feb 15, 2010 12:28 pm

raiken wrote:I think we may be getting to the real problem, finally... If original Marshalls are designed to sag 100V at full load (that's terrible regulation!), they wouldn't follow the original loadline/curves for a 480V amp, the curves would shift way down to the equivalent of a 380V screen amp running a 3.4K loadline, which would greatly reduce the signal swing/power dissipation/output.

Roe: what is your test equipment setup, here?

Do you have access to a signal generator, or are you just hitting a guitar chord and measuring the sagged voltage?

Do you have a scope to look at waveforms, or are you just measuring voltages with a multimeter?

Do you have a resistive dummy load, or are you running into a speaker when testing?

RA
Randall,

I dont have a signal generator (but could probably borrow one). I loop riffs with my DL4 delay box and measure sagged voltage with a multimeter. I'm running into a weber mass150 which is connected to a 1x12" cab.

I just borrowed a scope but need help of a friend to set it up :oops:
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Re: redplating 1959 w larmar

Post by Roe » Mon Feb 15, 2010 12:31 pm

VelvetGeorge wrote:The sag on our PT's is less, around half of that total drop under full output.

george
so the plate voltage should sag to about 430v with you 1203-80?
I got 450v when measuring with a multimeter
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Re: redplating 1959 w larmar

Post by raiken » Mon Feb 15, 2010 12:56 pm

Roe wrote:
Randall,

I dont have a signal generator (but could probably borrow one). I loop riffs with my DL4 delay box and measure sagged voltage with a multimeter. I'm running into a weber mass150 which is connected to a 1x12" cab.

I just borrowed a scope but need help of a friend to set it up :oops:
Download a software signal generator like this one, or do a search for one of the other free ones you can find on the web:

http://www.nch.com.au/tonegen/index.html" onclick="window.open(this.href);return false;

Run a 1/8" to 1/4" cable from your computer to the input of the amp and you can test the amp with a 1kHz sine tone to get a standard reference.

It would also be a good idea to build a standard resistive dummy load for testing.

RA

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Re: redplating 1959 w larmar

Post by Roe » Mon Feb 15, 2010 1:11 pm

raiken wrote:
Roe wrote:
Randall,

I dont have a signal generator (but could probably borrow one). I loop riffs with my DL4 delay box and measure sagged voltage with a multimeter. I'm running into a weber mass150 which is connected to a 1x12" cab.

I just borrowed a scope but need help of a friend to set it up :oops:
Download a software signal generator like this one, or do a search for one of the other free ones you can find on the web:

http://www.nch.com.au/tonegen/index.html" onclick="window.open(this.href);return false;

Run a 1/8" to 1/4" cable from your computer to the input of the amp and you can test the amp with a 1kHz sine tone to get a standard reference.

It would also be a good idea to build a standard resistive dummy load for testing.

RA
the signal generator software works. :D (need to find minijack though)

The only big resistors I have are:
1x 50w 16ohm
2x 50w 8ohm
This seems too little for this amp. but I could run resistors in parallel with the Mass150
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Re: redplating 1959 w larmar

Post by raiken » Mon Feb 15, 2010 1:24 pm

Roe wrote:
the signal generator software works. :D (need to find minijack though)

The only big resistors I have are:
1x 50w 16ohm
2x 50w 8ohm
This seems too little for this amp. but I could run resistors in parallel with the Mass150
Here's another free one:

http://heliso.tripod.com/download/generator/dsg.htm" onclick="window.open(this.href);return false;

The idea is to get rid of the Mass reactive load and use a fixed resistive load for accurate power measurements, so no, you can't run them in parallel with the Mass.

You could run the two 8's in series for 16 ohms, and run those in parallel with the 16 ohm for a total 8 ohm load of 100W, but that will likely not last very long if you are putting out the power it appears you are. You can try it for short tests before the resistors get too hot, but don't leave it on for more than a few seconds or they will start smoking!

RA

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Re: redplating 1959 w larmar

Post by novosibir » Mon Feb 15, 2010 1:26 pm

Roe wrote:the signal generator software works. :D (need to find minijack though)

The only big resistors I have are:
1x 50w 16ohm
2x 50w 8ohm
This seems too little for this amp. but I could run resistors in parallel with the Mass150
You can connect the both 8Ohm/50W in series, to get a 16Ohm/100W, but on a 100W amp output at full blast (square wave due to saturation will put out at least 141 watts) they won't survive very long.

You can try it, but I can't recomment to have the amp at full blast into 100W resistive load longer than about 5-10 seconds.
This should be enough time to measure the sag - and short enough, that the resistors don't turn into toast.

Larry


EDIT: Again RA was quicker than me - well, we Germans are slow :mrgreen:
The fault almost always is sitting in front of the amp :wink:

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Re: redplating 1959 w larmar

Post by raiken » Mon Feb 15, 2010 1:34 pm

novosibir wrote:
EDIT: Again RA was quicker than me - well, we Germans are slow :mrgreen:
Yes, but you're accurate. :)

RA

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Re: redplating 1959 w larmar

Post by Roe » Mon Feb 15, 2010 3:43 pm

finally got minijack so I could connect signal generator (PC) to amp.

with a 1k sine signal [and running into resistors] plate voltage sagged from 483v to 434v :) :wink:

that sounds about right given george's description above. it seems that the metro iron sags less than many marshalls. the amp sounds ballsy by the way. its ac/dc friendly: gimme high voltage rock n'roll, etc.
Last edited by Roe on Tue Feb 16, 2010 1:29 am, edited 3 times in total.
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Re: redplating 1959 w larmar

Post by Roe » Mon Feb 15, 2010 4:34 pm

VelvetGeorge wrote:...


Ground all output tube cathodes at a single point.
...

As suggested by George, I've moved the cathodes of the output tubes to one point (using larry's grounding scheme and twisting the grounding wires) [point 6 in earlier post]

EDIT: it appears to have no or little effect. v5 (RTF el34) redplates slightly with 10k tail resistor and 100k grid resistor at the PI input [this is still with the mass 150]

the el34 in v6 runs at 65%, v5 runs slightly cooler
Last edited by Roe on Tue Feb 16, 2010 3:04 am, edited 2 times in total.
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JTM45 RS OT JTM50 JMP50 1959/2203/34/39

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