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Low Voltage (60V) Stereo Tube Amplifier for Dummies (2+2W)
Low Voltage (60V) Stereo Tube Amplifier for Dummies (2+2W)
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Old 28th November 2014, 03:00 AM   #11
ballpencil is offline ballpencil  Indonesia
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Replacing the OPT with power transformer as mentioned, how much worse would the bass be from core saturation? I love the idea of low voltage single ended amp.. but having to source special transformer or going parafeed and double the voltage for CCS load are both uninteresting options. No choke loads for me.. might as well get the SE OPT.

Any cheaper option than PL504? Cheap Russian equivalent maybe?
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Old 28th November 2014, 07:52 AM   #12
bayermar is offline bayermar  Germany
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Just a quick question:
Would it make sense to run the power tube heaters directly with AC rather then after the recitifer? There would be less current on the bridge rectifier and therefore probably less noise (switching spikes) on the B+. The current demand of the 6SL7 heater is low and could also come directly from the 48V AC (dropped by a resistor) to even further simplify the design.

Just my two cents, though...

Martin
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Old 28th November 2014, 01:33 PM   #13
pilovis is offline pilovis  Italy
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Quote:
Originally Posted by ballpencil View Post
Replacing the OPT with power transformer as mentioned, how much worse would the bass be from core saturation? I love the idea of low voltage single ended amp.. but having to source special transformer or going parafeed and double the voltage for CCS load are both uninteresting options. No choke loads for me.. might as well get the SE OPT.

Any cheaper option than PL504? Cheap Russian equivalent maybe?
At this low voltage and low anode current, and if you choose a line transformer big enough (=> 40VA) you shouldn't have any core saturation, you might have some losses at low frequences due to the lower inductance of a line transformer respect to an audio transformer.

You might try EL36 (caution: 6 V heater!) or PL500 instead of PL504.

Quote:
Originally Posted by bayermar View Post
Just a quick question:
Would it make sense to run the power tube heaters directly with AC rather then after the recitifer? There would be less current on the bridge rectifier and therefore probably less noise (switching spikes) on the B+. The current demand of the 6SL7 heater is low and could also come directly from the 48V AC (dropped by a resistor) to even further simplify the design.

Just my two cents, though...

Martin
Sure you can, but I tested that the 50/60 hz noise is quite high when you use a.c. current for PL504 heaters.

Switching spikes? The power supply is working in linear mode, there shouldn't be spikes, consider also you have 1000 uF cap in parallel to the heaters.

This is a safe, cheap and funny tube amplifier for dummies to practice, you can safely use 6SL7, ECC81,82,83,85,88 or 6SN7 without risking anything, just check the correct pinout of the model you want to use and adapt it to this schematic.
The same for the tetrode, you can try PL36 or PL500 and listen to the differences ...

Starting from the point that an electrical device to be safe must stay below 60 Vcc or 48 Vac of supply voltage,
I choosed 6SL7 (6HC9 russian) because I found it to be the best solution for my ears with the values indicated on the schematic
I choosed PL504 because it is indestructible, works quite well at 50V and it is very easy to find on Ebay.
The output transformers should be in the range between 600 and 800 ohm, but again, you can safely use a trasformer with 1k or more to test it, the only risk is bigger distortion and lower audio volume.

A lot of times I found people that guiding principle was: "it shouldn't work" or "it is not theoretically correct", instead I found that some weird solutions worked very well, obviously it depends on what you want to obtain, if you are looking for an High End Hi-Fi amplifier, this is not the right project for you
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Old 28th November 2014, 02:11 PM   #14
artosalo is offline artosalo  Finland
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Quote:
Originally Posted by pilovis View Post
Sure you can, but I tested that the 50/60 hz noise is quite high when you use a.c. current for PL504 heaters.
Then you have something else wrong in your amplifier.
I have never had audible hum caused by ac-heaters of output tubes.
It is possible at the pre stages, if the implementation is poor, but not at the output.
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Old 28th November 2014, 02:23 PM   #15
pilovis is offline pilovis  Italy
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Quote:
Originally Posted by artosalo View Post
Then you have something else wrong in your amplifier.
I have never had audible hum caused by ac-heaters of output tubes.
It is possible at the pre stages, if the implementation is poor, but not at the output.
my hum problem was probably due to the very low space inside the box, heaters wires, even twisted togheter, are too close to the components and other connections inside the box, this is why I preferred using d.c. current for heaters.
Anyway, beeing this a practice project for dummies, by using d.c. current for all heaters we avoid any hum problem

Last edited by pilovis; 28th November 2014 at 02:40 PM.
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Old 28th November 2014, 04:31 PM   #16
nikon f is offline nikon f  United States
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Can you post a photo of inside the amp?
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Old 28th November 2014, 07:25 PM   #17
bayermar is offline bayermar  Germany
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Quote:
Originally Posted by pilovis View Post
Switching spikes? The power supply is working in linear mode, there shouldn't be spikes, consider also you have 1000 uF cap in parallel to the heaters.
My English term was probably not entirely correct (2nd language).
But your SS diodes switch off hard (Schottkys or plain vanilla UF4xxx versions might help). The 1000F cap is large (high charging current spikes) + heater current will create high EMF in the transformer = radiated noise (simple speaking).
AC is much more gentle here (no high dV/dt).

Martin
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Old 28th November 2014, 08:17 PM   #18
pilovis is offline pilovis  Italy
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Quote:
Originally Posted by nikon f View Post
Can you post a photo of inside the amp?
Maybe the box I used is too small, the main transformer inside the box becomes quite hot,
Inside the box there is also the 6Vcc power supply (small transformer + green pcb with rectifiers, LM317, resistors and caps), all other components are soldered directly to the tube sockets.
Click the image to open in full size.

else if you want a good Hi-Fi stereo tube amplifier you can try this one

*** Be careful: high voltages!

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Old 28th November 2014, 09:32 PM   #19
nikon f is offline nikon f  United States
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I am going to build the PL504 amp, and in the USA, can a 120/12 volt transformer be used as the OP?
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Old 28th November 2014, 09:56 PM   #20
pilovis is offline pilovis  Italy
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Quote:
Originally Posted by nikon f View Post
I am going to build the PL504 amp, and in the USA, can a 120/12 volt transformer be used as the OP?
yes

Z1=Z2*(N1/N2)^2

N1 = 120 (V)
N2 = 12 (V)
Z2 = 8 ohm (load impedance)

Z1 = primary impedance = 800 ohm

To avoid c.c. saturation use 40 VA (or more) transformer.

You can also try toroidal trasformer for halogen lamp (12V 5A or more) with very good results

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Hammond Mfg. - "Classic" 600 Ohm - Speaker Matching Transformer - Hammond P/N 119DA

Cost:under $40.00 U.S.

Low Voltage (60V) Stereo Tube Amplifier for Dummies (2+2W)


Ecc82 version with line transformers as the OPT

Click the image to open in full size.

Click the image to open in full size.

MP3 player + Ecc 85 version + Magic Eye as Vu Meter

Note: since the magic eye needs about 200 Vdc plate voltage, I used the 27 Vac from PL504 heaters with a small 220/24 V transformer reversed, swapping primary for secondary

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Ecc 83 guitar amp (mono) version

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How it sounds @ very low voltage (35Vcc) with ECC82 and line transformer as OPT

YouTube

stereo version @ 50 Vcc with 6FQ7 and line transformers as OPT

YouTube

just to avoid confusion since sometimes I use Vcc

Vcc = Vdc
Vcc = corrente continua (Italian)
Vdc = direct current (English)

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