Basic tube amp question(s)

Rolbista · Post by **Rolbista** » 04 Mar 2012, 17:49

Whoops, heaters seem to be at 9 volts! What does it mean? is it increased heater voltage that causes redplating? Would that be the reason for no sound? if 290V tap is indeed too highm what should I do? bigger resistors in the power supply?

deltafred · Post by **deltafred** » 04 Mar 2012, 17:56

Rolbista wrote:Whoops, heaters seem to be at 9 volts! What does it mean? is it increased heater voltage that causes redplating? Would that be the reason for no sound? if 290V tap is indeed too high what should I do? bigger resistors in the power supply?

Check that you are using the correct voltage tap on the transformer primary, the one that matches your supply voltage.

The heaters should be 6.3 volts AC. 9VAC is way too high and they will burn out very quickly. They are fed directly from the transformer so increasing the power supply resistors will make no difference.

diagrammatiks · Post by **diagrammatiks** » 04 Mar 2012, 18:01

I'd worry more about getting your readings correct first.

An amp running el84s like that should have no more then 400vdc on the plates.

6.3v on the heaters.

What voltage are your power supply caps rated at?

Rolbista · Post by **Rolbista** » 04 Mar 2012, 20:13

deltafred wrote: Edit
I don't know what your supply voltage is but to me it sounds like you are feeding 200 or more volts into a 120 volt tapping. Check this first.
edit/.

nope, that's not it, I only have one primary and it's designed for 230V, my wall voltage, I will check the (supposedly) 290V tap though, maybe it's not as tight as i thought it would. BTW, I sent the Ceriatone layout to the guy who made trannies for me so i kinda expected it to be just fine...

Edit/ Whoa, 290V taps read around 430- 450V each! I clipped black lead to chassis and touched the red one to wire from PT before rectifier diodes. @diagrammatiks caps are 450v onboard and 500V can cap on chassis (Tube amp doctor)

Edit2/ @deltafred so what now, stick a resistor in there? when i mentioned increasing resistors i meant the plate supply .

diagrammatiks · Post by **diagrammatiks** » 04 Mar 2012, 21:21

do you have a picture of your power transformer wiring?

Rolbista · Post by **Rolbista** » 04 Mar 2012, 21:49

i don't have any detailed shots of the wiring but i did everything according to the layout. The trannie has one yellow wire and one black coming from the primary and two thick blue wires paired with a thick brown wire and a set of two thinner red and one black wires coming from the secondary. I assumed that black and brown are ground, and thicker, blue wires are heaters because of higher current and the red are plates.

deltafred · Post by **deltafred** » 04 Mar 2012, 22:07

So let me get this right, you have only have only 2 wires for the primary, yellow and black.

It looks like the guy might have made a mistake when winding your transformer primary, putting too few turns on it.

I suggest you contact him before doing anything else as it certainly does not sound to have a 230v primary.

If you can get hold of a variac, a variable voltage transformer, then you could try bringing the voltage up until you get the correct secondary voltages. Then measure the input voltage.

No amount of resistors are going to make it right as you still need the same current but need to drop a lot of voltage which is all power that the mains transformer has to supply.

diagrammatiks · Post by **diagrammatiks** » 04 Mar 2012, 23:22

How did you wire up your mains connector?

Was there any documentation that came with your transformer?

where did you buy the transformer?

deltafred · Post by **deltafred** » 04 Mar 2012, 23:44

Ok I've done a bit of maths

The turns ratio of your transformer is approx the output volts / mains volts = 440 / 230 = 1:1.9
(You are getting 1.9v out for every volt you put in so it is a step up transformer with a turns ratio of 1:1.9)

So to get 290v out you would need to put 290 / 1.9 in = 152 volts in.

These figures may be quite inaccurate because of the unknown loading on the transformer dropping the output voltage. To do it properly the transformer should be loaded to it's rated capacity.

What you need is :-

For 290v out from 230v in you need a turns ratio of 290 / 230 = 1:1.26
(1.26v out for every volt you put in which requires more turns on the primary to lower the ratio.)

I am still of the opinion that he has wound you a 115/120v primary.

I missed the bit you wrote about plate resistors, I had assumed that you meant power supply dropper resistors, but the answer is still no. All the voltages are way too high.

diagrammatiks wrote "How did you wire up your mains connector?"

With 2 wires there are not too many options, one goes to live the other to return/neutral.

Rolbista · Post by **Rolbista** » 05 Mar 2012, 00:09

@diagrammatiks - i wired the connector just like on the layout, the trafos were wound by a guy named Ogonowski to my spec, people at a Polish forum recommended him to me. the only documentation was a sticker on the PT saying "Primary - 230V", "Secondary: 290-0-290V, 3,15-0-3,15V". @deltafred your theory makes sense, maybe the maker has made a mistake and wound the primary for 120V but thought he did for 230V. Anyway, i just sent him an email with my measurements hoping to shed some light. If he's persistent to help i'm gonna get angry though, cause i sent him the layout and schematic, and pointed out the voltages i want... And a variac is currently out of my reach, the cheapest one here is around 20$, and I don't even know if it would have enough power.

deltafred · Post by **deltafred** » 05 Mar 2012, 00:27

Rolbista wrote:... And a variac is currently out of my reach, the cheapest one here is around 20$, and I don't even know if it would have enough power.

You wouldn't want to be running permanently on a variac, it was just if you had access to one for testing purposes.

You have done the best thing contacting the maker.

It's a real bummer that the transformer is wrong.

Rolbista · Post by **Rolbista** » 05 Mar 2012, 11:49

So the maker of the PT called me today and told me to measure voltages on a bare transformer, disconnected from the circuit aaaaand (surprise, surprise) readings were still the same! Reported that back to him and he requested that i send it back and if the trannie is indeed not right, he will make me a new one. Nice of him but it's always annoying when something is wrong with a build, and it's not your fault!

phatt · Post by **phatt** » 05 Mar 2012, 12:14

Well do yourself a great BIG Favor and consider getting that transformer to deliver a Sane Voltage.

unless you like the idea of replacing valves every year ,,, stick to the correct voltages.

Power Valves should last for ~ 5,000Hours if run at sane voltages.
That means you would have to play for 13 hours a day to wear out a set of power tubes in one year.

You are shooting for 300VDC +/- 20percent.

Contry to BS sprouted by some EggSpurts there is little to be gained from higher than normal voltages.

I built a simple k biased Amp not unlike yours and it sings while running from 260VDC HT
I did build another one but it ran from 376VDC and guess what??? It was not as good.

You only gain a couple of watts (which is not audible) your tone gets harsher and your Valves will wear out faster. Go figure?

This might help you come to grips with power supplies.
Don't forget to Note the Current transfer difference with each type.

deltafred · Post by **deltafred** » 05 Mar 2012, 16:10

phatt wrote:... Power Valves should last for ~ 5,000Hours if run at sane voltages.

+1

I bought a 100w (4 X EL34) amp in about 1969 and gigged it continuously until 1997. In that time I replaced two output valves. At the time I had access to a valve tester so tested them regularly

kleuck · Post by **kleuck** » 05 Mar 2012, 16:30

phatt wrote:
Contry to BS sprouted by some EggSpurts there is little to be gained from higher than normal voltages.

Well, not so simple i think.
Without considering insane voltages like in the Mesa, and as you noticed, voltage has a huge influence on tone.
More straightforward, modern and cutting with higher voltages, more "singing" and soft with lower B+.
My VHT is running 6V6 at 350 volts (SE) or 300 as i put a switchable zener in the HV path.
The amp is more "musical" and vintage in the 300 volts mode (i call it..."vintage") but tested with a friend in the house in a little room, and outdoor, it's obvious that the 350 volts mod is better to cut trough in large rooms and with other musicians.
My mod involves the power and preamp obviously, but it would be the same, all other things being equal for a 5E3.
Another example : 1974X are great blues amps, where 2061 are great R'n R amps, and the one and only real difference is the insane voltage in the 2061.*
So, that's not a gain, you're true, it's a choice, matter of taste.

Rolbista · Post by **Rolbista** » 05 Mar 2012, 20:38

I was never my intention to change any voltage in this amp, i would be perfectly happy with normal one, but it appears that the manufacturer fucked up. it was supposed to be my first tube amp project, the only mods i was hoping to do someday were PPIMV and a simple fx loop. considered a tube rectifier but after all this mess with transformers i guess im gonna pass that one up. i'm afraid the OT will turn out to be bad either since i dont see any other reasons for which my amp should remain silent, i followed the layout very closely and used parts with high ratings just like you suggested at the beginning of this thread.

phatt · Post by **phatt** » 06 Mar 2012, 12:29

Hi Rolbista,
I believe you have a Speaker selector between the OT Secondary and the speaker? You may have wired it up incorrectly???? So Bypass it and wire the speaker direct to the appropriate tap on the transformer. I'd do that before assuming the transformer is at fault.

Phil.

phatt · Post by **phatt** » 06 Mar 2012, 12:35

kleuck wrote:
phatt wrote:
Contry to BS sprouted by some EggSpurts there is little to be gained from higher than normal voltages.
Well, not so simple i think.
Without considering insane voltages like in the Mesa, and as you noticed, voltage has a huge influence on tone.
More straightforward, modern and cutting with higher voltages, more "singing" and soft with lower B+.
My VHT is running 6V6 at 350 volts (SE) or 300 as i put a switchable zener in the HV path.
The amp is more "musical" and vintage in the 300 volts mode (i call it..."vintage") but tested with a friend in the house in a little room, and outdoor, it's obvious that the 350 volts mod is better to cut trough in large rooms and with other musicians.
My mod involves the power and preamp obviously, but it would be the same, all other things being equal for a 5E3.
Another example : 1974X are great blues amps, where 2061 are great R'n R amps, and the one and only real difference is the insane voltage in the 2061.*
So, that's not a gain, you're true, it's a choice, matter of taste.

Yes once you know your way around the landscape of valve land you can pull tricks but lets keep in mind that *Rolbista* is on his first amp and he has a far better chance of success if he sticks to the basics.
Let's not lose him to the world of reverse wound unobtaium gold plated silly stuff until he gets this one working.

Phil.

phatt · Post by **phatt** » 06 Mar 2012, 12:51

deltafred wrote:
phatt wrote:... Power Valves should last for ~ 5,000Hours if run at sane voltages.
+1

I bought a 100w (4 X EL34) amp in about 1969 and gigged it continuously until 1997. In that time I replaced two output valves. At the time I had access to a valve tester so tested them regularly

Yep You did well,,close to 30 Years

I doubt most of the Valve rigs sold today will still be working in 30 years time.

Phil

Rolbista · Post by **Rolbista** » 06 Mar 2012, 12:58

@ phatt - I'll try that, thanks, but what's bugging me is why is the OT CT (output transformer center tap?) connected to the 470 ohm resistor near the power supply? shouldn't it go to ground? i mean center tap primary, like in the assembly notes i posted. Also, just got a call from the maker of the PT and he claims to have measured it and says the voltages are fine... He mentioned something about a voltage doubler in my amp, i don't know what to think. Let's assume that my DMM measured incorrectly and the voltages were alright. why were the tubes redplating than? and the amp made no sound...? weird