• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

#26 pre amp

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#3,121
VR SHUNT REG

In my experience so far, I really like CCS + tube shunt (0C3 being the best),
I am using a headphone amp right now whit this arrangement and its dead quiet. I am always using very low capacitors to bypass the tube shunts...so on the order of 0.01-0,05uF. For 26 I will use only passive elements...a CLCLC configuration but the chokes needs to have around 30-50H. The psu output impedance is not so important for 26 tube...
 
#3,124
Hi!

Congrats for the beautiful build Felipe!

DIYspaceW said:
For 26 I will use only passive elements...a CLCLC configuration but the chokes needs to have around 30-50H. The psu output impedance is not so important for 26 tube...
Click to expand...

I agree! While you are at it you might want to try a pure choke input filter. I am using LCLCLC for preamps with the last LC separate for each channel

Best regards

Thomas
 
#3,128
kevinkr said:
Nice looking build Merlin.. 😀

About 12yrs ago I initially tried the VR150/0D3 in my early 26 based line stage design, but found the noise from the gas tube to be excessive in my application.. The plate to line transformers in question were UTC HA-133: 5:1 15K:600 which I am still using. The power amps had modest gain of about 10dB but were driving a rather efficient JBL speaker system (>100dB) wondering now whether I just had a batch of particularly noisy gas tubes.. (NOS) My opinion at the time was that it was almost quiet enough and had the speakers been about 6dB less efficient all would have been well.

My current speaker system is also over the 100dB mark so all of my electronics have to be extremely quiet.
Click to expand...

Thanks Kevin, today I experimented with mobile phone at less than 1 cm of the 26 = no noise, is incredible I was afraid of microphony and noise because all people in the thread told like a characteristic of 26. Can be your VR150/OD3 aren't good or I'm using other power transformer+choke (Bartolucci) also can be the OPT I'm use Lundhals LL1660, do you use Rod Coleman heater regulators?

You are right my speaker system have 94dB and also all my eletronics have to be quiet.

Greetings
Felipe
 
#3,129

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#3,139
bambadoo said:
Is it the shunt mod you are thinking of?
Shunt Pot Volume Control for Better Sound and/or Gain Reduction - World-Designs-Forum
An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
Click to expand...

Now I'm trying like attached pic, not exactly shunt but sounds very good, I use two 18k Shinkoh resistor and the improvement is big.🙂

What do you think about the resistor value for shunt type also 18-20K?

TIA
Felipe
 

Attachments

  • VolumePotParallelwiringdiagram mod 20K.gif
    VolumePotParallelwiringdiagram mod 20K.gif
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#3,140
amandarae said:
An externally hosted image should be here but it was not working when we last tested it.



My 26 Preamp. Thanks for this thread and the helpful guys keeping this thread as educational as can be.🙂

Abe
Click to expand...

Hello guys,

Just want to add info about the umbilical cord. It is about 5 feet using 300V/16Ga twisted and encased with braided shield for the B+ and 0V, 200V/18Ga twisted and individually shielded (per pair) for the two filament raw DC wires. 16 Ga Copper shielded for IEC and 18Ga shielded for chassis connections. All wires were then enclosed in black nylon jacket with all shields tied together.

Connectors are Neutrik NLT8MP (chassis) and NL8MPR(cord ends) with pins +/- 1 for heater 1, +/- 2 for Chassis GND and IEC GND, +/- 3 for B+ and 0V, and finally +/- 4 for Heater 2.

Enjoying the preamp as I type. 🙂


Abe
 
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