FPIII Resistance Check Results

[Frank Breech]

Hi, All,
My FPIII resistance checks are MOSTLY good.  Can anyone offer some advice on the #s that are off?  Particularly, the power transformer readings.  I think the Terminal Strips were close enough to be ok, but I listed the actual readings where they differed from the manual (and made them red, too) or wrote the word "Check" to indicate that my reading matched what was called out in the manual:
FPIII Resistance Check:

Power Transformer Terminal#/Required Resistance/My result:
1 infinity check  
2 infinity check
6 infinity variable gotten infinity a few times but also have had it counting down  and it doesn't seem to stop; also have seen it steady at 1.5 @ the 20Mohm MM setting
7 infinity        check
9 infinity variable - sometimes infinity, sometimes not
10 infinity variable - sometimes infinity, sometime not
4 variable        about 29 at the 200Kohm MM setting
5 variable         about 29 at the 200K ohm MM setting

Center Pins of RCA Jacks all check out ok.

Term#:   Resistance: My Result:
1   variable        Check
2 variable        Check
4 variable        Check
5 0 Ohms        .2 (at 200 ohm scale setting)
6 variable        INFINITY
7 variable        check
9 0 Ohms        .1
10 variable        Check
11 470K        check
12 variable        Check
15 22.1K        22.2K
16 0 Ohms        check
17 15K        check
19 0 Ohms        check
20 33K/Infinity        Check
21 variable        Check
22 33K        31.5K
24 0 Ohms        Check
25 variable        Check
26 33K/Infinity         Check
27 33K/Infinity        32.9K
28 0 ohms        Check
29 33k/infinity        Check
30 33K/infinity        Check
31 22.1K        22.2K
32 variable        check
35 470K        Check
36 33k/infinity        Check
37 15K Ohms        Check
39 0 ohms Check
40 0 ohms Check

Thanks, in advance

Mike

 

[Grainger49]

Mike,

Infinity doesn't have to be infinity.  I think Dan says that above a Megohm is to be considered infinity.  Variable and infinity are the results of capacitors in the circuit and their charging.

Different meters give different readings.  Take a quick look at FAQ question #7:

http://www.bottlehead.com/smf/index.php/topic,2408.0.html

You need only worry about readings that are +/-15% out of spec.  

It appears to me that you are ready for the dreaded smoke test.

 

[Frank Breech]

Dear Grainger, thanks, as usual for your replies. 

As you know by now, I'm a little nervous about the smoke test; as a result, I have mixed feelings about your last post, indicating it might be time.  Indulge me for a few more queries about the readings I listed, if you will:

RE the Power Transformer Resistance Readings
Transformer Terminals 4 + 5:
Should I be concerned that these should be fluctuating according to the manual but have held steady at the #s I listed below?

Transformer Terminals 9 + 10:
Unfortunately, I didn't write down what reading I was getting for these two, but since my meter seems to react to infinity fairly definitively on other terminals, should I be concerned that terms 9 + 10 are sometimes variable (never settling down while taking the reading)?

Transformer Terminals 1 + 2:
These puppies never climbed a bit then jumped to infinity -- when my test leads aren't touching anything, they are at infinity (reading the air), when I touch them to terms 1 + 2, there is no change, just stays at infinity, no jumping, no signs of life, as it were, in the meter.  What do you think? Almost seems like it didn't register that there was any kind of connection.  I'm still kind of new to the multimeter though - only ever really used it for continuity testing, so maybe this is totally normal.  Can you confirm?

Signed,
Nervous in the North East

 

[Grainger49]

The easy ones are transformer terminals 1 and 2.  They have no ground reference, have no current path to the ground buss or chassis.  So they should be a wide open infinity to ground.

Transformer terminals 9 and 10 are just like transformer terminals 6 and 7.  Look on page 7 of the manual. The two 150V windings are 6/7 and 9/10.  The windings are wired such that the top leads are together and the bottom leads are wired together.  So what you get on 6 you measure on 9 too.  What you get on 7 you measure on 10 too.

The schematic shows resistors and capacitors to ground that should charge and give you a rising resistance.  Once you do that you can prove that it is working by swapping the red and black leads. I usually get a negative resistance reading as the capacitors discharge.  

For the heater leads, transformer leads 4 and 5, are the tubes out of the circuit?  Are you reading a dead 29 ohms or 29k ohms from each terminal to ground?  Does it change when you swap the leads?

And since meters read differently, what meter are you using?

If in doubt post a picture of the transformer wiring.

 

[Paul Birkeland]

These resistances look good.  Between the seven multimeters that I have, they will all display the infinity values differently. 

The other minor variations are not concerning.  22.1k vs. 22.2k could simply be meter tolerance or some resistance encountered in measuring.  What you're generally looking for in the resistance checks are zeros where you don't want them, or high values where you want zeros. 

-PB

 

[Frank Breech]

Paul,
Thanks for these confirmations.

Grainger,
I'm going to be able to get at the unit later this afternoon, I think.  Until, then, the questions I can answer for you are:

RE The Heater Leads (Transformer terminals 4, 5): The tubes were in place while I took these readings. (They were in place for ALL of the readings I took and listed) Is that how it should be?

RE my Multi Meter: Here's a link to a copy of the manual:
http://hitechhub.com/pdf/1101.pdf
Funny, if you go to Triplett.com, there's a little product slideshow embedded into the homepage.  If you wait 15 seconds or so, the MM I have, the 1101-A will show up as a "featured product." However there is no mention of it, save for a carrying case, that shows up in a search of the website.  There is a newer 1101B, however.  But, the 1101-A is also NOT included in the legacy equipment manuals page.  Annoying.  Anyhow, all the info you would probably need about my MM is available at the URL above.

I will try your other suggestions when I get back to my desk.

THanks!

 

[Grainger49]

Mike,

When the tubes are installed the heaters are a dead short.  But the capacitor is expected to charge.  I wouldn't worry about your readings on the transformer readings for the heaters.  The old manual I have say that the tubes should be in place.

I have used Triplett meters in the past.  I trusted them as a Simpson or Fluke.  I expect you are seeing the individual meter reading thing for a capacitor in the circuit.  It is expected.

I think you are ready for the smoke test. 

 

[Frank Breech]

Ok.  I try it soon.  I lost my alligator clips so I've got to go get some new ones. 

I'm reading the instructions and on page 37 it says:
"Switch the meter to read DC volts"  and "Voltage (VDC unless otherwise specified)"
Then the first 5 readings it calls for are labeled "VAC" off of transformer terminals 4, 5, 6, 7, 9.
My question is: Should the MM still be set to VDC to make these readings?

-Mike

 

[Doc B]

"unless otherwise specified" -  switch the meter to VAC to measure VAC.

 

[Frank Breech]

Hi, All,
Did my smoke test without getting hurt.  All the terminals read well within 10% of what they should be, except for the power transformer.  This is what i got:

PT term
4            64  (Should be 3.3VAC)
5            same as above
6            498 (shoudl be 165.5)
7            496 (shoudl be 0)
9            498 (should be 165.5)
10          225DC (should be 0)

I tried my MM set to both VAC scales available "500" and "200".  They both read the same

IS is possible something is wrong with my MM?  I mean: would all the other terminals throughout be just about spot on if the PS was actually this far off of the correct readings?

Thanks in advance, as usual.

Mike

 

[Doc B]

You are OK. Those voltage numbers are expressed in a fashion that doesn't exactly correspond to what you really measure. In other words for AC measurements you would not really read 0 and 165, you would read 165AC from one transformer terminal to the other, the black lead would not be connected to ground. The reason it is labeled 0 and 165 is obscure, it has to do with which end of the winding is the "start" and which is the "end", something that doesn't really matter to a kit builder with a set of instructions that tells what wire goes where.

At any rate if the voltages on the tube sockets are right, it's working as designed.

 

[Frank Breech]

Doc, Thanks for this info.  I appreciate the quick reply -- as you can imagine, I can't wait to plug this in and also get started on my Eros (sitting right next to me still in the box!).

All other voltages are almost perfectly matched to the numbers suggested in the instructions.  Thanks again

Mike

 

[Frank Breech]

Hi, Guys,
Brought my FPIII home on Friday night and listened to it quite a bit.  It's a big change (for the better) from my SS preamp.  It's hard to describe the difference, and I guess I don't have to to anyone here on this forum ... but as my first experience with a tube component on my home system I am extremely impressed with how it really seems to bring some more personality out of my speakers (B&W 704).  It's loud - but i'm not sure I want to tweak the sweetest whispers to change this, it's sounding so nice.  It's hard to describe but it's not just loudness but rather a kind of powerful feeling.  I'm not using an SPL meter, but at basically the same listening level I had been used to with my SS pre, I feel a kind of energy coming through now that I did not have before.  I'm really curious about what the upgrade kit can do, now.  On just about everything I listened to, I heard some details I never had before - I can't ask for much more than that.  A couple of potential issues are:
1. I don't think my 12AU7 tubes are glowing at all.  Should they be bright? (at least as proportionately bright as the OD3?)  They definitely get pretty warm. 
2. My right sweetest whispers pot is noisy when rotated.  Sounds like a dirty pot.  A couple of times the right channel (on all 3 inputs) would not be as strong (volume wise) as the left at the same sweetest whispers setting - then it would get better -- like it was drifting. 
3. I think there was one more thing but I'm blanking out right now ...

Thanks a lot for all the help.

Mike

 

[Grainger49]

Mike,

The overwhelming response to the Extended upgrade is, "I didn't think my FP III could sound better but I was wrong!"

1) 12AU7s don't glow that much.  Since you have good sound everything is as it should be.

2) First try runnng the SW up and down with it off to clean the contacts.  If that doesn't work try spray contact cleaner.

As for the padding resistors to give you a finer volume control... try some without wrapping them through the terminals.  Just kind of tack solder them on first.

When you find a good resistor that lets you get to 3:00 on the SW swap the supplied resistors for $4 designer resistors.  A good $10 tweak when you include shipping.

 

[Frank Breech]

Grainger,
I'll try some contact cleaner this evening.
A question about further tweaks:
When I start going back under the hood on this thing, now that's it's been powered up a bunch of times, how worried/cautious do I have to be around the capacitors?  I know they can present a danger, but don't understand if the need to worry is completely obviated by the bleeder resistors that are installed.  Also, I've never handled capacitors before this, is the "outside" dangerous?  That is, would the only way to get a shock from them be to touch the two terminal probes at the same time?  Can it be potentially dangerous just to touch the outer part (the battery like barrel/body of the units)?
Thanks!
mike

 

[Doc B]

I believe that this is the kind of thing best learned if you learn from experience. Nope, I don't mean touch your tongue to the terminals...connect your voltmeter across the terminals of one of the filter caps and turn the amp on. Leave it on for a minute so the cap charges up, and then turn it off. Watch how long it takes the voltage to get down to, say, 10 or 20V as it bleeds off. Once you do that you will have a good sense of how long you need to wait before the bleeder resistors have completed their job.

 

[Grainger49]

Mike,

The bleeder resistor in the power supply will remove the voltage quickly.  

If you want to be sure throw your meter across one of the big power supply capacitors before getting your fingers in any dangerous places.

The outside of the capacitor is safe.  It is not connected to either lead.  Edit: see below.  Although none of the capacitors I have seen on Bottlehead equipment has a capacitor lead connected to the can it is not a guarantee that it may be connected in the future.

You got it, you have to touch both leads, or the + lead and the chassis at the same time to get hurt.

 

[Paul Joppa]

Grainger, that's not always true. Many capacitors, especially electrolytics, have the case connected to the negative terminal. Since it's a voltage doubler power supply, some of the caps have above 200 volts DC on the case.

Gun people say "always assume a gun is loaded until you have personally checked, and then only until you turn your back". Same for high voltages is my rule. It takes only a moment to check; if you have the amp upside down you probably also have the meter at hand!

 

[Grainger49]

I know that the multi-capacitors in cans on old tube amps use the outside for the common of 2-4 internal caps. 

Are you saying the caps in the FP III use the can for the common?

 

[Frank Breech]

Thanks. 
I will do the test and watch the caps charge up, then watch them bleed. 

So, now I know that it can be dangerous to touch the case of certain caps.  Specifically, is the FPIII one of those cases?  I promise to proceed with caution no matter what the answer.  And I'll never turn my back on them. 

I tried contact cleaner on my SW a little bit ago ... no luck.  Any suggestions about what to do to quiet them down?

Thank You
Mike