Basic tube amp question(s)

RnFR · Post by **RnFR** » 17 Jan 2012, 04:20

HT = heater transformer?

kleuck · Post by **kleuck** » 17 Jan 2012, 07:26

Sorry, i'm french so HV for High Voltage rail

("Haute Tension" in french)

Schematic is here : https://www.freestompboxes.org/viewtopic ... hilit=kiss
But there's not a lot of gain, i plan to build this (PSE) one :

RnFR · Post by **RnFR** » 17 Jan 2012, 08:05

OK makes sense now!

btw- whats that mic in the pic in the other thread?

kleuck · Post by **kleuck** » 17 Jan 2012, 08:14

Cheap chinese mic trying to emulate the Senheiser 606 : Superlux (Avlex) PRA628.
New model here : http://www.thomann.de/fr/superlux_pra_628_mkii.htm
Not as good as the 606 obviously -less lows, you have to use the proximity effect to get a somewhat flat response, but totally worth the price.

Rolbista · Post by **Rolbista** » 30 Jan 2012, 15:58

ummm, another basic tube amp question rose up. On the layout http://www.ceriatone.com/images/layoutP ... Layout.jpg there are markings N, E and L. What wre they? Also, I have only two wires coming out of my primary winding, a black one and a yellow one, the socket has 3 pins though... should I bridge twe two lugs and leave the E one for ground? Secondary windings have center taps I solder them to ground on the chassis, right? The heater wires will be thicker because they carry more current right? And there are two grounds in the picture, why is that? I only made one grounding point...

kleuck · Post by **kleuck** » 31 Jan 2012, 23:43

"E" is for Earth indeed, so ground, no connection to the PT.
On the layout, the centre tap of the PT goes to ground trough the HT fuse, beware not to forget it.
The two ground are not mandatory, but i suppose, easier to wire.
The thicker wire has to be for the heaters yes.

Rolbista · Post by **Rolbista** » 04 Feb 2012, 10:51

Another question, I want to put a PPIMV on my amp, am I right thinking that all I need to do, is to put a dual ganged pot between 2k7 resistors, and power tubes and the other lug solder to ground? If yes, then what value should the pot be? 250K like people suggest in most online threads or something else?

DrNomis · Post by **DrNomis** » 04 Feb 2012, 10:58

RnFR wrote:HT = heater transformer?

Actually no, HT is short for "High Tension", basically it's another name for the High Voltage supply rail found in Tube/Valve amplifiers.....

Rolbista · Post by **Rolbista** » 02 Mar 2012, 18:24

ehhh, put the amp together, plugged into a cab and guess what? No sound. The indicator lamp lits up (it didn't at first, but it turns out the light bulb was just disconnected), ALL of the tubes glow (preamps a little, power a bit more, i think they look like they should). There is no sound, no hum, hiss, noise, nothing. Tried another cab and another speaker cord - still no sound, another guitar cable - no sound, checked guitar volume pots even - they were ok. I've just read some on the internet about debugging an amp if it makes no sound http://www.geofex.com/ampdbug/glow.htm , but the problem is all parts are new: tubes, speaker, transformers, pots, nothing was recycled, nothing was mysterious trash bought for cheap, so a perspective of swapping all the tubes right away, or replacing a transformer kinda scares me. by the way, it was the first power-up ever. for pics of internal wiring jus go here: http://www.elektryczny-banan.blogspot.c ... warta.html Any help? please.

deltafred · Post by **deltafred** » 03 Mar 2012, 00:08

Rolbista wrote:... N, E and L. What are they? ...

UK mains labelling, and possibly other countries.
L - Live
N - Neutral
E - Earth

Live is the hot mains wire in the UK it is typically 240VAC.

Neutral is the cold or return wire. It is connected to earth at some point but due to volt drop along the power lines may be a few volts above earth so keep it away from the Earth connection.

Earth is connected to the earth. Connect this to your chassis.

deltafred · Post by **deltafred** » 03 Mar 2012, 00:35

Rolbista wrote:... Any help? please.

First check the HT fuse.

If that is ok then (very very carefully, see below) check the voltage between points A, B, X and Y and the chassis. They should be several hundred volts, not sure exactly how much but a lot.

Clip the meter common (black lead) to the chassis and using your right hand* carefully probe the points A B X Y. Put your left hand behind your back or in your pocket to stop it touching anything earthed.

(* Advice I was given as an apprentice when working on high voltage equipment. Using your right hand minimises the risk of current flowing through your heart should you accidentally touch something that has high voltage on it. Others have a more relaxed attitude to working on high voltages, the choice is yours but I still follow what I was told by my lecturers at college and seniors at work.)

Report back with your voltage readings.

deltafred · Post by **deltafred** » 03 Mar 2012, 11:58

On the subject of safety have a read of this before you start fault finding.

http://www.aikenamps.com/SafetyTips.html

Rolbista · Post by **Rolbista** » 04 Mar 2012, 13:46

i'm not sure how should i measure the resistance of the OT, and in what range? my amp is push-pull, so should i first measure, say one red lead from the power tube to for example to 8 ohm tap, repeat for all taps and then the second red lead to all taps? i read the instructions on GEO site but don't quite understand... Voltage readings are as follows: around 530V on A and B, 450V on X and 480V on Y. Fuses are fine, the amp smells a little after a while, not smoke or burns but like something getting hot quickly, maybe just tubes getting their work temperature, but i don't know. I'll attach a pic of how i wired the OT, maybe it's just a stupid assembly error?

phatt · Post by **phatt** » 04 Mar 2012, 14:13

Forget the OT.
Something is very very wrong!!!

EL84's where designed to run around 300VDC,,, you have 530VDC.

Of course you do have your DMM set to read DCVolts don't you?
Valves are voltage tolerant devices but not when taken to extremes.

Yes they do seem to be glowing ,, check you have under 7VAC on the heater pins.

Phil.

Rolbista · Post by **Rolbista** » 04 Mar 2012, 14:17

when i started checking powertubes voltages (live amp) i did the same, black lead to chassis, red to every pin of the tube, here are the readings:
1st pin - 0V
2nd pin - 0V
3rd pin - 19V
4, 5 and 6 nothing
7th pin - not sure on this one, but DMM showed something like 530 for a second? again, this is not the best DMM in the world...
9th pin crazy numbers constantly changing
Also, when i touched some od 4, 5, 6, 7 and 9 pins, there appeared some noises in the speaker, like crackilng and sparkling, i also felt a smell of something getting hot so i stopped the test.

sorry for the double post, just ran out of time to edit it

phatt · Post by **phatt** » 04 Mar 2012, 14:39

Did you switch your meter to read AC Volts on pins 4/5?

*Deltafred* has already mentioned safety but I should ADD;
Most cheap DMM's Are not meant to be used on big voltages such as Valves.

Do yourself a very big favor,,,,, if you value your life go get one that is CAT Rated for the voltages you wish to measure.

As to the Amp the 19 Volts DC on the cathode lines up with a high plate voltage.
Check if the plates are starting to glow red,, If so then the Power Valves are way beyond their rated limit and over dissipating and will die in a short time.
Phil.

diagrammatiks · Post by **diagrammatiks** » 04 Mar 2012, 16:32

well your tubes are definitely redplating.

Rolbista · Post by **Rolbista** » 04 Mar 2012, 16:59

ok, I'll get a better DMM from a friend, but what could cause an amp to make NO sound? From my humble knowledge i assume that this happens only when somewhere the signal is shorted to ground... I'll also try to replace preamp tubes when i get some, but if something was burnt up from too high voltage during the first powerup ever, wouldn't it break down pretty apparently? Like, smoking, burning, breaking glass? Anyway, wouldn't power tubes with too high voltage just sound more distorted or something instead of silence? I mean, they should 'sound' somehow at all, right? Even when too hot. The OT doesn't get even warm, but maybe i shouldn't take it for granted because the amplifier only ran for a few minutes every time so far.

deltafred · Post by **deltafred** » 04 Mar 2012, 17:28

Forget replacing the preamp tubes, the voltage is way higher than it should be and you need to find out why and get it down to a reasonable level.

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/

290VAC out of the transformer should give you no more than 410V DC at point A.

When you get your CAT rated meter set it to AC volts and measure the voltage between the chassis and the transformer 290v outputs (or on the outer ends (anodes) of the diodes) if this is more than a few % more than 290VAC then investigate why.

You might have the wrong transformer for your mains voltage or are using the wrong primary tapping.

Rolbista · Post by **Rolbista** » 04 Mar 2012, 17:47

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?