Tube Amplifier and Tube pre-Amplifier Builds

[radium7]

Instead of opening several threads, I will post all my Tube related projects in this one. Hope this will be useful for other DIYs and members. I’m posting the information after I tested and confirmed. I welcome fellow members to share their ideas and comments.

The Christiansen "DG" 300B Amplifier

I’m building this Amp for a FM. You can find all details of this amp in their website.

It consists of a Power supply board, Driver board, Maida HT regulator board, Filament regulator boards- 3 nos

The power transformer is a custom made one. The output transformers are from Onetics ltd, USA.

Input transformer from Jensen Transformers. The input stage with transformer is the best and i like this type of circuits.
In the first stage the preamp tubes are LED biased. Negative bias output stage.

We planned to build this amp in wooden chassis with top cover 14 SWG Copper sheet, back and bottom covers are MS sheets.

Almost the construction of the amp is completed, except the 5V filament regulators for 300B tubes not yet received. waiting for it
.

 

[radium7]

Compared the operation of Tom Christiansen filament regulator with Chinese made buck converter.

Tom’s is excellent the voltage rises gradually and constant at 6.3V. No heat emitted from the IC. But in Chinese buck convertor rises suddenly to 6.3V and the IC emits heat after few seconds.


Maida Regulator


Driver Board with Jensen Input Transformers (Photo taken during testing-Led glows)


Power supply Board


Testing the Amp with chinese regulator board

 

[tuff]

Good stuff. Tubes are coming back with a vengeance.

 

[Beast_of_burden]

Excellent. Why wooden box, wouldn’t a metal box be better for lowering noise? Are you using shielded cable for the signal wires? Can you disclose name of aforementioned FM for whom this is being built?

Instead of opening several threads, I will post all my Tube related projects in this one. Hope this will be useful for other DIYs and members. I’m posting the information after I tested and confirmed. I welcome fellow members to share their ideas and comments.

The Christiansen "DG" 300B Amplifier

I’m building this Amp for a FM. You can find all details of this amp in their website.

It consists of a Power supply board, Driver board, Maida HT regulator board, Filament regulator boards- 3 nos

The power transformer is a custom made one. The output transformers are from Onetics ltd, USA.

Input transformer from Jensen Transformers. The input stage with transformer is the best and i like this type of circuits.
In the first stage the preamp tubes are LED biased. Negative bias output stage.

We planned to build this amp in wooden chassis with top cover 14 SWG Copper sheet, back and bottom covers are MS sheets.

Almost the construction of the amp is completed, except the 5V filament regulators for 300B tubes not yet received. waiting for it
.

I am interested in this kit. Onetics OPTs are nothing to sneeze at. Please see my PM.

 

[radium7]

Vacuum tube volt meter servicing

This BPL VTVM belongs to my Tube Amp Guru. It is in working condition but requires few maintenance.
The voltage measurements are correct and ohms section that is used to measure resistor valves are not accurate. so i decided to find out the problem and rectify it.

It has two sections bottom have the circuits and top have tubes, transformer and one battery that is required for ohms section. All the components are original never changed so far. Film capacitors are mullard mustard and most of the resistors are 1% high precision resistors. Only one electrolytic capacitor. The battery is damaged due to age and the electrolyte capacitor need replacement.

Both capacitor and battery changed, and it is back in action. Now it is in full working condition. Its very sensitive. I always love to see swing of pointer in analog meters.

After some cleaning

 

[sunilj]

Hi, any progress on your 300b ?

 

[Hari Iyer]

Imo the layout of the components could be challenging for de bugging in case of servicing required. Mounting on terminal blocks could resolve some of the issues.

 

[radium7]

Completed and tested the DG300B Amplifier. work delayed due to a faulty regulated board, now replaced with new one. This is one of the very very quite DHT amplifier I have build so far.
The sound is different it’s not like vinyl tube amp (sweet but lacks in frequency range) and not like modern tube amps (very accurate but lacks in sweetness). It has sweetness with lot of detail. Important thing, it does not have much fancy branded components except the input transformer (Jensen). Here quality of sound depends on the operating points of the tubes and the way the voltage and current are regulated. Maida regulator, filament regulator and CCS are the main the reason for quality. Really amazing.

Few drawbacks in it.

Very low input sensitivity (3.9 Vrms) - need a good preamp with high output.
PCB’s design may need few improvements. Maida regulator and power supply PCB’s are fine.

The driver board which has the CCS will generate lot of heat. The heat sink of CCS is on the pcb and soldered to the pcb. When the heat sink is heated the heat transferred to the pcb and the heat affect the soldering spot of the components. Also heat the components in the pcb and it will affect life of components.

Need more space between the components in the pcb and need space to have big heat sink.

During testing the amp i operated the amp continuously for more than 3 hours with full load; there is no damage in it (soldering spots). When i switched off it and touch the components and pcb they are noticeably hot.

Need lot of ventilation in the amp and a good air conditioned room.

Regarding the sound quality this amp is a Gem

 

[radium7]

 

[radium7]

Hi, any progress on your 300b ?

Now building a JE lab preamp. after that will start that work.

 

[radium7]

Imo the layout of the components could be challenging for de bugging in case of servicing required. Mounting on terminal blocks could resolve some of the issues.

yes it is difficult, using lug strips or eyelet boards makes it better.

 

[sunilj]

Now building a JE lab preamp. after that will start that work.

Good going. Would like to hear your experience before I go down the path.

 

[sunilj]

P.S: Whats the driver on that Onken cabinet ?

 

[radium7]

P.S: Whats the driver on that Onken cabinet ?

12" Philips fullrange- not alnico, ceramic magnet but very good ones. The mid from this speaker is unbeatable.

 

[pksnathan]

Nice finish though i cannot speak of technicalities.Is this amp mono or stereo?Please let me know.
Thanking you.
pksnathan

 

[radium7]

Nice finish though i cannot speak of technicalities.Is this amp mono or stereo?Please let me know.
Thanking you.
pksnathan

Its a stereo power amp, need a good preamplifier.

 

[radium7]

JE Labs Preamp with phono section

6SL7 tube for phono
76 and 6SN7 tubes for Line stage
5Y3 Rectifier tube

Phono section is battery biased. Line preamp section have 76 tube as first stage and one triode of 6SN7 tube is used as second stage of line preamp.
Although 76 and 6sn7 tubes have very close electrical parameters they are different in sound signature.
lot of informations are availiable in internet about this circuit, so there is need to go deep.

Power supply section and preamp section are in separate units like the original design.
power transformer and choke are custom made locally with good quality materials and to exact spec.
Metal oxide, carbon composition(AB), carbon film (Takman and few NOS) resistors are used.
F&T, Elna cerafine, Russian pio capacitors used. Need to buy few more capacitors.

 

[radium7]

 

[radium7]

Choke fully sealed

 

[radium7]

Power Supply chassis