2555 voltages issues. help

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gmule12
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2555 voltages issues. help

Post by gmule12 »

Hi 🙋 every one. This is my first post and l hope l will get some help. So I build a ceriatone kit 2555 . The problem with voltage is that looking on Nik layout point HT CT where chock is wire to the electrolytic capacitor, the voltage is 432v and not 470v according to voltage chart. I did some test by taking valves out and voltage go up to 509V so that is ok. I'm using dagnal transformers from TAD. l also changed the tap from 240v to 230v ,little improvement but HT didn't move to much. Any suggestions folks. Thanks.
sluckey
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Re: 2555 voltages issues. help

Post by sluckey »

That's only 8% low. Easily accountable because you used a different PT. Bias setting will also affect this voltage reading. If you bias the tubes cooler that voltage will increase. I would not be concerned about that voltage difference.
Stevem
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Re: 2555 voltages issues. help

Post by Stevem »

A Marshall like this model never had 470 volts at idle, what is your voltage with the tubes all in with the amp in standby?

What is the level of AC voltage into the rectifiers with the tubes in and the amp in standby?

Also having all the tubes out and 509 volts on filters rate for only 509 is not a good thing for too longed!
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Not screaming like the passengers in his car!😊

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gmule12
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Re: 2555 voltages issues. help

Post by gmule12 »

Voltage chart the one I have is from ceriatone web say 470v . As far voltage with tube's in ,is 440v max . And at rectifier, with tubes is 190x2 . My mine problem is about the feel in response and thin and little bit fizzy low frequency.The tone is far away from smooth you really have to work to get any half decent tones. Amp is far away to be transparent. It's sound like covered with blanket. I have to keep treble an presence almost on max So I'm trying to get voltages writ before any thing else. If you ask. Yes l build the kit my self and it's not my first.
gmule12
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Re: 2555 voltages issues. help

Post by gmule12 »

I mean fizzy high frequency. And my bias is 37mv and -38. Sorry English is not my first language.
gmule12
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Re: 2555 voltages issues. help

Post by gmule12 »

I also want to ask you, will make any difference to the voltage or respond and feel of the amp, if I did swap to wires coming out of OT transformer going to power tubes pin 3 . I'm asking because Nik layout have different colours and colours on TAD transformers was different. Maybe stupid question.
Stevem
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Re: 2555 voltages issues. help

Post by Stevem »

440 volts sounds about right for what I would expect with the output tubes idling at .035 amp. Or 35 milliamps depending on how you want to look at it.
Lack of highs with harsh cranked tones could be caused by many things so take all of your voltage measurements first and report back.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
gmule12
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Location: Belfast

Re: 2555 voltages issues. help

Post by gmule12 »

ok this is my voltage's

pin 1 pin 3 pin 4 pin 5 pin 6 pin 8
v1 246 1.9 215 1.5
v2 226 1.6 118 0.4
v3 256 39 250 39
v4 37 mv 437 431 -39 436
v5
v6 any below is the same
v7


idle is 440 and voltage at standby switch is 2x190
thanks for your time mate.
Last edited by gmule12 on Thu Oct 05, 2017 8:04 pm, edited 1 time in total.
gmule12
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Re: 2555 voltages issues. help

Post by gmule12 »

:cry: Hello.Hello.
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pompeiisneaks
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Re: 2555 voltages issues. help

Post by pompeiisneaks »

Okay first off that seems pretty confusing. You should not have those readings on the first preamp tubes, as pin 4 and 5 are heater pins and should read 6.3VAC.

Maybe your pinout list is the error, but I also could be mistaken on what's going on here. Was there a schematic listed? Are the preamp tubes not 12A*7 types?

~Phil
tUber Nerd!
gmule12
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Re: 2555 voltages issues. help

Post by gmule12 »

Sorry for error, the v1 is the first pre-amp tube and it is 12AX7 .
maybe this will help as I thing l have one power tube with very bad bias reading, my bias is set 37mV but one tube has 51 mV .
l took out two tubes and the voltage go up in HT to 470V but that is normal as there is no two tubes and the 470V is on Nik voltage chart . i'm going to send them back and report if all 4 good tubes will keep the voltage HT at min. 465V
Stevem
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Re: 2555 voltages issues. help

Post by Stevem »

How are you reading this output tube bias voltage, by means of having a voltmeter hooked up across a 1 ohm resistor going to ground from Pin 8 ?

One output tube pulling more current than another is just a good sign of a stronger tube!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
gmule12
Posts: 34
Joined: Tue Dec 06, 2016 11:46 pm
Location: Belfast

Re: 2555 voltages issues. help

Post by gmule12 »

Yes It is. Ceriatone has external bias port on the back. And 1R resistor, way?
gmule12
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Re: 2555 voltages issues. help

Post by gmule12 »

But if you think about resistor bad grounding. I swap tubes a cross and the reading was the same as in the first tube socket.
Stevem
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Re: 2555 voltages issues. help

Post by Stevem »

In regards to the output tubes that 1 ohm resistor allows voltage and current to be read the same , so you should start thinking in terms of amps when using those rear chassis mounted test points.
Your posting of the output tubes idle state should be for example .037 amp, or 37 milliamp whichever you preference.

And as replyed to you, your voltage readings from your preamp tubes look messed up !
Pins 4 and 5 should be tied together for 6.3 vac heater , so a heater wire should be on these two pins and one on pin 9.

On the v1 and v2 only pins 1 and 6 should have more than 180 vdc on them.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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