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Old 3rd March 2010, 11:04 PM   #1
Minion is offline Minion  Canada
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Default Some general tube questions from a Tube newbie !!

Hi Guys , Im prety new to tubes but have done a lot of Solid state stuff so Im not new to electronics so I have some general tube questions a questions about some Mystery tubes I have so I can attempt a tube project (guitar amp)......

1 I was wondering about Grounding , specificly , do you tie the heater Ground and the plate ground together ?? And if not were does the audio ground go ??

2 What is the output AC Voltage (audio signal) of a Tube like a 12ax7 at full gain ?? Does the Voltage go up considerably after several Tube stages or does it just hit a certain clipping threshold ??

3 I found a busted home made Tube amp that has some tubes in it that aren"t really labeled and was wondering if you guys might have a clue what they are....

The first one has 5 Pins and has UY above 76 inside a stop sign shaped circle , its shaped like 6V6 but about 25% smaller .....

The other one is the same size and shape but has 6Z above P1 inside a stop sign shaped circle , but this one has 6 pins .....

There is one more that I cant find right now but I think it is a rectifier tube as it only has 3 pins ....

The amp also has a small 6 in speaker and a small output transformer and a small power transformer .......


Thanx Guys !!!
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Old 4th March 2010, 06:28 PM   #2
Arnulf is offline Arnulf  Europe
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Quote:
Originally Posted by Minion View Post
1:) I was wondering about Grounding , specificly , do you tie the heater Ground and the plate ground together ?? And if not were does the audio ground go ??
Depending on the tube used. With indirectly heated tube you can leave it floating or tie it at a fixed positive potential. With directly heated tube you have no choice but to tie it to ground at one point.

Quote:
2:) What is the output AC Voltage (audio signal) of a Tube like a 12ax7 at full gain ?? Does the Voltage go up considerably after several Tube stages or does it just hit a certain clipping threshold ??
Amplification factor of 12AX7 is 100 in theory and somewhere between 55-60 in practice. Output swing depends on input swing and supply voltage (it cannot go past supply rails, obviously).

The followup question makes no sense (to me at least): of course the voltage goes up in cascaded stages with gain larger than unity and of course it can get into clipping eventually.

Quote:
3:) I found a busted home made Tube amp that has some tubes in it that aren"t really labeled and was wondering if you guys might have a clue what they are....
Photos will go great length further than text description.
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Old 4th March 2010, 10:38 PM   #3
Minion is offline Minion  Canada
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Hi , Thanx for the explanation but now I"m more confused than before ....

What is an Indirectly heated tube as opposed a directly heated tube ??

I only know about takeing a seperate winding off the transformer and either Powering the Tubes heaters with AC or rectified Filtered DC , and was wondering if I tie the DC Heater ground to the Plate supply ground , or if I use AC do I just leave it floating ?

My question about output voltage and clipping has to do with in solid state you go into clipping when the output voltage approaches the supply voltage , But in tubes the Supply Voltage is upwards of 350v so it wouldn"t go into clipping till it appraches 350v , which would take quite a few tubes at max gain and a 200mv guitar signal to get it to clip but we all know you can get a single tube to clip, as they do in many guitar amps .......

So that was why I was asking , also if I wanted interface a High gain Tube preamp with a solid state Power amp I would need to know what type of output Voltage I would expect so I could suitably Pad it down .....?

As for Pictures of the Tubes I can"t do that as I am one of those loosers that doesn"t have a camera as I can"t justify spending money on something I will use once a year, but there is absolutely nothing on the tubes accept for what i described .....

Maybe I need to ask this differently , what types of tubes have 5 pins ?? and what type of 6 pins ?? (EG: Triode , Pentode ect)

Thanx a Lot ....Cheers
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Old 4th March 2010, 10:55 PM   #4
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Quote:
Originally Posted by Minion View Post
Hi , Thanx for the explanation but now I"m more confused than before ....

What is an Indirectly heated tube as opposed a directly heated tube ??

I only know about takeing a seperate winding off the transformer and either Powering the Tubes heaters with AC or rectified Filtered DC , and was wondering if I tie the DC Heater ground to the Plate supply ground , or if I use AC do I just leave it floating ?

My question about output voltage and clipping has to do with in solid state you go into clipping when the output voltage approaches the supply voltage , But in tubes the Supply Voltage is upwards of 350v so it wouldn"t go into clipping till it appraches 350v , which would take quite a few tubes at max gain and a 200mv guitar signal to get it to clip but we all know you can get a single tube to clip, as they do in many guitar amps .......

So that was why I was asking , also if I wanted interface a High gain Tube preamp with a solid state Power amp I would need to know what type of output Voltage I would expect so I could suitably Pad it down .....?

As for Pictures of the Tubes I can"t do that as I am one of those loosers that doesn"t have a camera as I can"t justify spending money on something I will use once a year, but there is absolutely nothing on the tubes accept for what i described .....

Maybe I need to ask this differently , what types of tubes have 5 pins ?? and what type of 6 pins ?? (EG: Triode , Pentode ect)

Thanx a Lot ....Cheers
Hi,
Iam a newbie too. In direct heating the AC or DC heats the Cathode itself, and in the Indirect Heating the AC or DC voltage heats a filament near the Cathode that heat the cathode by radiation(no physical contact).
For HiFi use DC heating is best sound and more expensive, maybe in guitar amp you can use AC heating.
This is my two cents, Gustavo
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Last edited by FullRangeMan; 4th March 2010 at 11:14 PM.
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Old 4th March 2010, 11:09 PM   #5
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Quote:
Originally Posted by Minion View Post
Maybe I need to ask this differently , what types of tubes have 5 pins ?? and what type of 6 pins ?? (EG: Triode , Pentode ect)
Quote>> Maybe I need to ask this differently , what types of tubes have 5 pins ?? and what type of 6 pins ??
Looks it could be a Single Triode or a Single Pentode respectively...
The Double Triode 12AX7 family have 9 pins, Single Triode like 572/211/845 power tubes are 4 pins.
Regards, Gustavo
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Old 4th March 2010, 11:26 PM   #6
Minion is offline Minion  Canada
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Hi , Thanx , I just found a bit of info on the tubes I have, They are Old Japanese tubes , the 6ZP1 I believe is a Pentode as it says it is good for 1w output , and the UY76 is a single triode , there is Very little info on these tubes on the net accept in Japanese which doesn"t Translate well ....

I"ll just scap the idea of useing these tubes and just use the Power transformer for a 12ax7 Tube preamp project ......

Maybe someone will help with my other questions ....


Thanx
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Old 4th March 2010, 11:32 PM   #7
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Quote:
Originally Posted by Minion View Post
What is an Indirectly heated tube as opposed a directly heated tube ??
I know it's tempting to ask a series of questions, since there's a seemingly endless source of replies out here, but simple questions like this, and quite a lot of more complex ones, can be answered for yourself with google.

Yes, valve amplifiers clip. If you think about it tho', they use high voltages. This means small currents (otherwise the powers would be very large), and that means high impedances compared with solid state circuits (in general). It means transformers to drive speakers. Interstage voltages and currents all need to be planned tho' to meet the requirements of the various stages.

If you can design a SS amplifier, then you can probably plot a load line. If you plot a load line on a valve characteristic, you can see the input and output voltages, and the voltage gain, etc., etc. Again there are tutorials on this and simulators, some dedicated to valves.

w
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Old 4th March 2010, 11:52 PM   #8
Minion is offline Minion  Canada
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I can see that this is going to be futile ..... Thanx
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Old 5th March 2010, 09:56 AM   #9
Arnulf is offline Arnulf  Europe
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Quote:
Originally Posted by Minion View Post
I only know about takeing a seperate winding off the transformer and either Powering the Tubes heaters with AC or rectified Filtered DC , and was wondering if I tie the DC Heater ground to the Plate supply ground , or if I use AC do I just leave it floating ?
This question doesn't make any sense. If it's a directly heated tube, you can't leave its heater supply floating, otherwise the circuit won't be completed and no current will flow. If it's an indirectly heated tube we're talking about you can do either.

Quote:
My question about output voltage and clipping has to do with in solid state you go into clipping when the output voltage approaches the supply voltage , But in tubes the Supply Voltage is upwards of 350v so it wouldn"t go into clipping till it appraches 350v , which would take quite a few tubes at max gain and a 200mv guitar signal to get it to clip but we all know you can get a single tube to clip, as they do in many guitar amps .......
This is not a question, this is a statement, and confusing one at that. I can't think of a way to get a single 12AX7 stage to clip with 200 mV p-t-p input and 350V anode voltage (nevermind exceeding the maximum rating ...) in a simple common cathode configuration. But yeah, if a tube with sufficiently high amplification factor was used and the load presented to it was very large, it could go into clipping with 200 mV input (think pentode + CCS load).

Quote:
So that was why I was asking , also if I wanted interface a High gain Tube preamp with a solid state Power amp I would need to know what type of output Voltage I would expect so I could suitably Pad it down .....?
Depends on tube, topology and exact component values; the only correct answer would be "any and all". Anything from 0V to about as much as anode supply voltage is doable (peak to peak).

Quote:
As for Pictures of the Tubes I can"t do that as I am one of those loosers that doesn"t have a camera as I can"t justify spending money on something I will use once a year, but there is absolutely nothing on the tubes accept for what i described .....
Perhaps your mobile phone has a camera ? Most of these come with one nowadays, under reasonable light it will substitute for the real thing just fine.

Quote:
Maybe I need to ask this differently , what types of tubes have 5 pins ?? and what type of 6 pins ?? (EG: Triode , Pentode ect)
It doesn't work this way - there are different types of bases, UX5 being an example of 5-pin base and "27" (triode), ""47" (pentode) etc. being examples of different tube types using same UX5 base. This is not unlike solid state world where you can find BJTs, diodes, FETs, complex ICs, triacs, thyristors, etc. all tucked into same plain TO-220 package.

You need to determine tube type by its name and/or manufacturing code, then we might be able to give you answers that pertain to your tubes only and not to tubes in general (which is what you're asking now).
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Old 5th March 2010, 04:42 PM   #10
kevinkr is offline kevinkr  United States
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@ Minion

Go out and get yourself a copy of Morgan Jones "Valve Amplifiers 3rd Edition" as this will give you a very solid foundation upon which to build your understanding.

Presumably having dabled with solid state you understand the very fundamentals of electronic theory - if not you should probably study up on Ohm's Law, Thevenin's and Norton's theorems, and the behavior of inductors, capacitors and resistors as a minimum..

Good construction practices can be learned from you guessed it: Morgan Jones "Building Valve Amplifiers"

For anyone who loves audio electronics these two titles are extremely entertaining reading, and IMHO if anything is a must read these titles are it.

Online (Pete Millett's site, etc.) look for old Norman Crowhurst articles. Back issues of Audio Amateur, Glass Audio, and the current AudioXpress are also sometimes good sources of newbie learning.

Most of all don't give up! Building your first tube project will be rewarding as you learn how to do things, and finally get it working. There will be plenty of help here..
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