the Poor Man 660 support thread

[Gus]

tommypiper I do not think there is anything wrong with the unit I spent hours on the phone with Kevin.  The currents are about what they should be we measured voltages and calculated currents using Ohms law via voltage drops at certain resistors.

I also gave Kevin a change to drop the heat in the IRF820.

I don't think the tubes are bad they might be "to good".

Pay attention to the links I posted you might note the tube is often used in a pulse amp.

http://www.mif.pg.gda.pl/homepages/frank/sheets/131/6/6900.pdf  Look at the top right and read the page.

read about the gm of a 6900
http://www.vacuumtube.com/issue5.htm

http://www.mif.pg.gda.pl/homepages/frank/sheets/127/5/5687.pdf  note high emission

Pulse amps are an on off circuit that need to pass "enough" current, so a "better" pulse amp tube might exceed the specs so it can be used as a sub.

Has anyone else measured there Edcor transformer temp?

 

[tommypiper]

OK, Gus now I'm confused.  Kevin says the tubes were his main problem.  You're saying you don't think his tubes are bad.  And you think his unit is fine.  Therefore, what is/was causing his problems, if it's not his tubes and not his unit?  This logic is self-contradicting.  What are we missing here?

Are you saying the tubes are the wrong kind for this application?  If so, then why are there so many successful builds in operation with these tubes?

Has anyone else had problems with bad tubes? 

Kevin was shipping off his tubes for testing.  How did those tube tests come out?

I don't understand.

 

[Gus]

IIRC Doug was the first to note there are 5 tubes in the GE book with a 9H base.

The question is what was a 5687 type tube designed for?

I looked them up in my GE book
7892 specs are pulse amp no rp or gm even listed just 5amps 25% duty cycle
7370 20 or 40volt fil
leaving three look them up at Franks tube page
6900 (note generic 5687 on the PDF)
7044
5687

The tubes causing the issue are possibly "to good" I don't think they are bad.  I am SURMISING the tube was not designed for audio amp duty and that they were designed are pulse amp tubes as best I can tell because what is printed in the PDFs.
Gm (look up the definition of transconductance)and High emission and Pulse amp on the spec sheet are a hint.

Now one tube operation MIGHT be a good thing and the tube MIGHT work fine and last.   A "better" tube still meets the min specs of 5687.  Maybe a 6900, 7370 is marked as a 5687

The real issue is the we did not have a good sample size of the 5687 tubes characteristics until people built the circuit and Kevin asked questions, then others that had this issue removed one tube in the sidechain amp and the unit worked like it should.  The weirdness could be explained by saturating of the output transformers and having stray magnetic fields affecting the meters.

The transformer heat issue could be as simple as using a >=8amp fil winding OR adding a separate transformer for the vamu stage tube fils to remove some of the load on the main transformer.  The complete unit heat issue can be address by layout and venting It might need a bigger box.

Power into the box has to equal power out of the box(power out of the box is the audio and all the heat) Put a power meter inline with the unit like a  P3 "Kill A Watt" and look at the power used watts, power factor etc.

One other thing is it could be some kind of feedback path causing an oscillation this could be seen using a oscilloscope.  IIRC Doug posted about this.


EDIT
Transformer heat issue FIX a higher fil current transformer or add another fil transformer for some of the fils to reduce the load on the existing transformer.

Enclosure heat issue FIX design a different layout and venting maybe a fan etc.  You just can't stick stuff in a box and not think about the heat issue with a build like this.

tube issue FIX Select the side chain tubes

IRF820 heat FIX change a resistor value (Kevin did you try this yet?)



Tommypiper what don't you understand?

 

[khstudio]

OK, Gus now I'm confused.  Kevin says the tubes were his main problem.  You're saying you don't think his tubes are bad.  And you think his unit is fine.  Therefore, what is/was causing his problems, if it's not his tubes and not his unit?  This logic is self-contradicting.  What are we missing here?

Are you saying the tubes are the wrong kind for this application?  If so, then why are there so many successful builds in operation with these tubes?

Has anyone else had problems with bad tubes? 

Kevin was shipping off his tubes for testing.  How did those tube tests come out?

I don't understand.

No offense man but I'm not sure what or how else to say what I'm going thru... I've explained it in FULL detail many, many times.

When you build your unit & if you have any of these issues I'm sure you'll go back & read more thoroughly what was said.

One more time:
#1 - My meter was acting strange
#2 - My Cathode voltages were fluctuating when turning the Threshold
#3 - My PT was getting hot

So... I went thru the unit testing for every possible problem for a week or 2 until eventually pulling one of the "side chain" tubes.
This fixed #1 & 2

So... I then ordered a NEW, DIFFERENT Brand of 5687's to try those (Tung-Sol) & they worked fine using a PAIR, as opposed to the Philips 5687's that did NOT work as a pair.

Gus is saying that ANY of these 5687 tubes can be within spec but possibly out of spec for THIS unit... like he just mentioned "maybe too good" because of what they were originally designed for.
Rowan is supposed to get back to me about sending him a tube to test but he has been very busy, so I wouldn't count on that for a while.

This leaves me with #3... a HOT PT.

End of story.

 

[CJ]

this chi town nos xfmr for the f670 is like a box car, if that is any help.
i have to wear a waist band just to move the dang thing.

 

[MartyMart]

this chi town nos xfmr for the f670 is like a box car, if that is any help.
i have to wear a waist band just to move the dang thing.

CJ - "NAIL ON THE HEAD" comes to mind, I think it's time we all accepted that the PWR Traffo's are
under spec for this project AND .....  if "working" then right at the limit of what they are supposed to do/supply.

Tube issues are accepted, perhaps wrong batch / type or even mislabeled, so some have got lucky with
the ones they have. ( Kevin's new set are fine which is great news )
I just hope that my Euro pwr traffo and Tubes can perform their duty ..... when I get there !!

MM.

 

[radiance]

I'm curious if there are any people who finished their unit with the "non Edcor" groupbuy power tranny (with the 6A heater sec) AND who are using the slow start heater psu boards. Question for those people: how hot is your power tranny and  what voltage + curent are you meassuring after the slow start psu boards??

 

[dagoose]

I think the hot tranny might also have something to do with the 220/110v differences in europe/usa.
Mine is running warm but certainly not hot. I didn't measure the temp but it feels comfortable warm, something like ''nice during winter to warm you cold hands''.

I have like 5,9 volt max with a stereo unit and with regulated/softstart boards. I doesn't matter if i hook up one board or 2 to the tranny so it looks like the tranny is ok but it's the regulator that has a problem with voltage drop with running the tubes. When i just power up the heater boards without anything connected 6.3v is no problem and i have some 'headroom' as well, not sure how much but way more the 6.3v.
But so far no problems with the 5.9v at the the tubes so i'll just leave it this way for now.

 

[stanz]

I want to throw a word of caution out here in regards to Kevin's hot pwr transformer. Be careful that you are not confusing symptom with cause. Just because the transformer is hot does not mean that it is what is wrong. I say that because I have not seen anyone else state they have had an issue with the Edcor pwr transformer. It could very well be your problem (6A heater supply seems low), but until you have eliminated all other variables, do not focus just on it as your problem.

An easy way to eliminate it as an issue would be to hook up a separate heater supply transformer and see what happens. It will tell you one way or the other if that is your problem.

 

[CJ]

they  added heater transformers onto the stock pwr supply, i think there are one or two extras, probably added for the exact same reason.

the guy at aes said he had the most trouble with the choke in the low voltage supply.

had a problem getting enuff turns on the core.

 

[kazper]

they  added heater transformers onto the stock pwr supply, i think there are one or two extras, probably added for the exact same reason.

the guy at aes said he had the most trouble with the choke in the low voltage supply.

had a problem getting enuff turns on the core.

The PoorMan uses 4 or 8 valves, over the X many the original used. CJ it may be a work a round or a necessary evil to make the project function using split transformers for those late on the show.


Kev,

Besides that is there a issue with the power supply that could be loading you up? How hot is the bridge and does it need more meat to it's mounting?

I'm ordering up the last bit of parts for my PM460/470 this week, for 2 stereo and one mono set. I do have 4 of the original transformers from Edcore 2 of the wrong secondaries that they didn't want returned and 2 of the replaced units. So I may have some voltage reading to compare with later this week possibly. I also have 3 PSU pcb's so I can try some combination but that is probably a two weeks or so out before I may be ready.

What does the current specs call out for the 8 valves? I believe the 6 Amps was supposed to be plenty but I don't have time to back track the threads, if not maybe the transformer can't really push that close to it's max.

 

[Holger]

... Question for those people: how hot is your power tranny and  what voltage + curent are you meassuring after the slow start psu boards??

Pretty much the same as dagoose. Some 5.6/5.8V for after start up. My Rondo transformer gets warm but not hot.

 

[radiance]

Pretty much the same as dagoose. Some 5.6/5.8V for after start up. My Rondo transformer gets warm but not hot.

Well, if it works....

....still not understand what's happening though. A regulator is supposed to give the voltage it's been set too right? Might it be that the voltage drops (from 6,3V to 5,8) due to the transformer not being able to supply the needed current? It would be more logical that an underspec-ed trannie becomes too hot...

 

[kazper]

Simple ohms/watts law, something is going to give to balance out the equation and voltage drops etc... may be it.

What about the resistor, that's primarily there to drop the voltage down to the 6.3V. 5.8V, Is (R15) sized correctly ? I would think that the adjustment (R15) would have to be made with Tubes in circuit, to help adjust for the load of the tubes....  Or the fact that your not getting any more electrons down conductor lane and like said before your loosing potential to make up.

 

[radiance]

Simple ohms/watts law, something is going to give to balance out the equation and voltage drops etc... may be it.

Well, that might be the case when not using the regulator boards.

But what happens to a regulator (in this case the LM338) when the transformer is not able to supply the current drawn by the heaters? Is it as simple as lowering the voltage to make up for less current?

 

[khstudio]

I want to throw a word of caution out here in regards to Kevin's hot pwr transformer. Be careful that you are not confusing symptom with cause. Just because the transformer is hot does not mean that it is what is wrong. I say that because I have not seen anyone else state they have had an issue with the Edcor pwr transformer. It could very well be your problem (6A heater supply seems low), but until you have eliminated all other variables, do not focus just on it as your problem.

An easy way to eliminate it as an issue would be to hook up a separate heater supply transformer and see what happens. It will tell you one way or the other if that is your problem.

If you were to say this a few weeks ago I'd probably agree with you but not now.
I'm not sure if you missed what I posted but I've gone thru extensive testing, measuring & troubleshooting.

- Using "ohms law"... Gus & I went thru the entire unit & it's running as it should.
- The power supply is getting & putting out the correct voltages.
- The heat of the PT goes up & down depending on how many tubes I have installed. (see the the chart I posted a page or 2 back)
- I ran the PT with NOTHING connected to secondaries = no heat!
- I ran the PT with just the Power PCB connected to secondaries = no heat!
- Then connected just the heaters = this is when the PT starts getting hot.

It could very well be your problem (6A heater supply seems low)

you said it & this is what I'm focusing on now. 

 

[kazper]

from the data sheet:

A unique feature of the LM138 family is time-dependent current limiting. The current limit circuitry allows peak currents of up to 12A to be drawn from the regulator for short periods of time. This allows the LM138 to be used with heavy transient loads and speeds start-up under full-load conditions. Under sustained loading conditions, the current limit decreases to a safe value protecting the regulator. Also included on the chip are thermal overload protection and safe area protection for the power transistor.

http://www.national.com/ds/LM/LM138.pdf

There is temperature of the chip at play, Voltage differential and some other factors on where that limit is going to be.

 

[khstudio]

Kev,

Besides that is there a issue with the power supply that could be loading you up? How hot is the bridge and does it need more meat to it's mounting?

Yes... the Bridge Rectifier gets very hot & is mounted on the side of the case with silicon added.

The temp of the Bridge Rectifier also goes down when I pull 2 of the 5687's

 

[kazper]

Whats the Data sheets call out for the current on the valves?

6BC8 = 0.4A
5687 = 0.9A
x4 = 5.2A

Where running it at 86%.

Any chance we could skip the Resistor on the 5687 and give it higher voltage, it's specked to 0.45A on a 12.6V heater?

 

[khstudio]

Whats the Data sheets call out for the current on the valves?

6BC8 = 0.4A
5687 = 0.9A
x4 = 5.2A

Where running it at 86%.

Any chance we could skip the Resistor on the 5687 and give it higher voltage, it's specked to 0.45A on a 12.6V heater?

I was thinking along the same lines... 12v heaters = less current draw.
BUT - I don't think the 9v secondaries of the Edcor will cut it... we need more juice.