First build is alive.

[declan]

Here are some pics of my first amp build, I couldnt believe it when i fired her up on the bulb limiter and things started checking out. Unfortunately I have a cheap DMM which has been giving strange readings at the top end of its scale so i did not dare go any further than check voltages and a few second strum. Some of the B+ voltages are reading high so I intend to sit down with it next week with a decent meter before going any further.

I havent posted many questions here as most of the answers I needed so far were but a search away but I fear that it is now getting to the limits of my competence, so I will ask forgivness now for any stupid questions you guys have to suffer over the next few weeks.

Heres #1

If my bias voltage range is too low is it the 220k resistor across the PT secondaries that needs lowered?????

First fit in her Cab, ..... the cab is being left with a friend next week who does wood burning art... I have no idea yet what i am going to ask him to do..

[declan]

more shots

[Ron Worley]

Hey Declan-

I had apparently weird stuff happen with the limiter- but they were uniformly low voltages. The limiter keeps everything uniformly low. So it's intentional that it works that way.

If they're high, then somethings amiss...

Ron

[declan]

Ron,
I didnt note everything down, but without the limiter,

secondaries 620v
heaters 6.4v
Bias Min -31.5v
Bian Max -20.8v

Some B+ voltages were reading significantly higher than expected and when i tried to measure plate voltages the meter refused to stabilise so i stopped there.

with the limiter they were all a little lower as expected

The same meter refuses to accuratey measure 1m resistors or anything else on its highest scale settings so I am hoping that the DMM is the problem, although it could very well be me.

[gearhead]

A couple of suggetions that might be useful:

1) Get yourself a decent, but cheap multimeter to measure voltages when the amp is on. They're accurate enough for that purpose. Get mine from the local computer mega-mart. 6$ on sale. I have a tendency to blow one up per build.

2) Measure, write down, and type here All your voltages, starting from the input at the switch (the 120V range):

Power In: VAC
PT Secondary: VAC

Bias - VDC

Heaters: VAC Tap to Tap


All the rest are VDC:
B+1
B+2
B+3
B+4
B+5

V1a plate
V1a cath
(tonestack driver)


v1b plate
vab cath
(first input from jack)

v2a plate
v2a cath

v3a plate
v3a grid

v3b plate
v3b grid

V3 common cath

V4 plate
V4gs
V4 grid in -

V5 plate
V5gs
V5 grid in -

[Ron Worley]

Hey Declan-

I agree with Gearhead- If you look at page 45 of my build guide, I provided a chart to write all of these values down, along with some typically expected values for the main (non-tube) voltages.

Hopefully that will help. 620V seems high, I was told that the secondaries should be around 585V. Your bias min should be up around -35V too...The more experienced here will know for sure.

Ron

[declan]

couldnt wait and bought a mid range meter today (as i suspected my DMM was at fault), all voltages check out as per your charts Ron. I have a bias min of -38 to a max of -23. so loads of scope.

Biased the tubes .... cranked her up and .... Oh MY GOD!!!!

for me, anything worth saying about the experience of playing one of these amps is best left at that for now.

I am back to play with her this evening, and put a few mullards and a set of winged c into her, I have a quad of siemens I will leave until I am happy everything has settled in.

She seems to be fairly well behaved with no strange oscillations noise or hum (that i have noticed) so far...... but the feedback sustain and touch sensitivity..... im not saying any more... all who have one of these amps know..... nothing could take the smile of my face at the minute

thanks to all you guys for this fantastic resource, I could not have build her without this place.

Ron i didnt have your guide for the build but it sure was useful for testing, so a special thanks to you

[declan]

double post oops

[Ron Worley]

No sweat, glad at least some of it helped...

I broke down years ago and bought a very good fused Fluke meter.. it has been worth every cent. It autoranges, so no resetting, measures capacitance, checks diodes and so on... I think I got it on ebay new for ~$125 or so.... wish I had two for transformer shunt biasing..

Also glad that you really didn't have a problem...

+111 on the first time you hear it live....I think I yelled "Holy $hit" out loud when I fired mine up.

RLW

[declan]

wish I had two for transformer shunt biasing..

so do I Ron...... thought i killed her tonight doing this. Ended up stripping down the tube socket and cleaning the burn marks, and testing absolutely everything from scratch.

I have absolutely no idea how nothing got fried apart from the DMM fuse .... a very hair raising experience i will take great care never to repeat again.

I wasnt getting a mv reading and tried to scratch through the surface when the probe slipped.... the real problem was lack of attention to the fact that the other end of the probe was in DCV socket not mv. I should have avoided the tempation to "scratch" and went back and checked.

Two avoidable and simple mistakes could have cost me a lot more than a fuse.

I am posting this for the benefit of anyone who is either not familiar or becoming complacent with this bias method.

If you can't follow every single piece of safety advice on transformer shunt biasing, and add a large helping of common sense with the patience to check and double check what you are doing ..... my advice is use another method.

I'm no EE, but I've worked inside live equipment of one sort or another for many years, Unfortunately it seems to take a near miss every decade or so to keep me on my toes and on this occasion anticipation got the better of me. I think i will retire in about 8 then.

[Ron Worley]

Frankly (because I'm not a pro tech, or build for a living), I get a tad nervous every time I bias and have to reread my own build notes...

I can't claim to be related to Leo, so even though I do have an EE degree, it's about practice and experience...

I also use the spring clips on my leads to insure that I minimize the potential for hitting a hot tube lug....

I want to have a second meter so that I can spring clip leads from two meters for plate and cathode voltages using my bias resistor box... or set it up for the Tranny shunt verson.....

Call me a pussy, but it only takes one killer shock to end the game permanently...

Ron

[skyboltone]

Frankly (because I'm not a pro tech, or build for a living), I get a tad nervous every time I bias and have to reread my own build notes...

I can't claim to be related to Leo, so even though I do have an EE degree, it's about practice and experience...

I also use the spring clips on my leads to insure that I minimize the potential for hitting a hot tube lug....

I want to have a second meter so that I can spring clip leads from two meters for plate and cathode voltages using my bias resistor box... or set it up for the Tranny shunt verson.....

Call me a pussy, but it only takes one killer shock to end the game permanently...

Ron

Once in the morning does it Ron

[rooster]

Hey Ron - I did take a serious look at your documented build file and it was very very helpful - THANK YOU!! I think you covered everything needed for almost anyone.

I, too, have finished up my first Express build tonite. I am waiting for my custom PEC volume pots from Canada before I do the actual sonic play. Yeah, hard to contain myself but the pots should be here tomorrow. As to voltages on a new build, skyboltone, that 600VDC is way too high for the Tone Sluts PT I have here. There must be some measurement mistake or a very bad meter. Doing the power up via Variac, with no tubes installed, my #1 B+ is 398VDC, very appropriate for a finished plate voltage of 390 I think but we'll see. And man, that TS PT is one big piece of iron. And you mentioned the 220K resistor? I think I am going with 150-200K here because I would rather see a range of -28VDC to -40VDC. I could be wrong but I am pretty sure this - 220K - is not going put me in the middle of my expensive pwr tubes. We'll see.

Anyway, this is not my first build of an amp, but I will admit that this is a very complicated little build in regards to the pwr supply. I have never done anything quite so bizarre - and here drawing from my past amp building experience - as stacking a bunch of caps together and siliconing them to the chassis. !! And yes, I have seen plenty of Matchless amps with the same thing, but have never done a build this way. Ron, I see where you avoided this? And I almost did, too, but finally caved. To me, it is this one facet of the build that makes it a more difficult build. This being said, I do like the way Komet layed their pwr supply out? Knowing that KF was there with them makes me think that even he had morphed his build technique away from such, hmm, 'simplicity'.

Which is to say if there is an issue with one of these builds, I am pretty sure where I would look to find the problem, eh?

So, OK, tomorrow then for me. And Ron, your lugs worked out very well, thanks again. skyboltone, congrads!

[skyboltone]

, skyboltone, that 600VDC is way too high for the Tone Sluts PT I have here. There must be some measurement mistake or a very bad meter.

I think we're mixing threads and ideas here. I mentioned in another thread that a Hammond Organ AO-35 PT and a toneslut express PT have the same 300-0-300 secondary voltages but that the Hammond measures 255 ohms across the secondary and the toneslut is likely about 60 ohms. I don't think I made mention to voltage. Just that one can expect a 1:1.5 ratio with a full wave rectifier with the hammond and a 1:1.38 with the Toneslut with tubes lit and biased.

[gearhead]

, skyboltone, that 600VDC is way too high for the Tone Sluts PT I have here. There must be some measurement mistake or a very bad meter.

I think we're mixing threads and ideas here.

And I was thinking you had edited your thread!

Now you will see about 600 VAC at the secondary of the PT.