Going to be building the Mullard 3 tube 3 watt amplifier from the mallard book.
Here's the print. Mullard 3-3. Three Watt Amplifier
question-
I have a pair of single ended 5k transformers that have 4/8 and 16 ohm taps. In the print they have a 1k resistor across the output of the output transformer to ground, Which if you look at the print is R14. If I have 4/8 and 16 ohm taps do I omit that resistor or just put it between 16ohm to ground?
Here's the print. Mullard 3-3. Three Watt Amplifier
question-
I have a pair of single ended 5k transformers that have 4/8 and 16 ohm taps. In the print they have a 1k resistor across the output of the output transformer to ground, Which if you look at the print is R14. If I have 4/8 and 16 ohm taps do I omit that resistor or just put it between 16ohm to ground?
I suspect its there just to ensure there is some load in case a speaker goes open circuit. In which case it needs to be across the OPT outputs - any will do.
Mullard also published a similar amp of lower power based on the 6BM8/ECL82. I worked with member Jeff Yourison in revising that design. It may make sense to contact him for some notes and building experience.
You definitely can save quite a bit of money by emulating the B+ supply Jeff and I used. "Full wave" voltage double the O/P of a low cost Triad N-68X isolation transformer. As the N-68X has dual primaries, it is useful just about everywhere other than Japan. The 100+ mA. of B+ that can be extracted from a N-68X should be more than adequate.
You definitely can save quite a bit of money by emulating the B+ supply Jeff and I used. "Full wave" voltage double the O/P of a low cost Triad N-68X isolation transformer. As the N-68X has dual primaries, it is useful just about everywhere other than Japan. The 100+ mA. of B+ that can be extracted from a N-68X should be more than adequate.
feedback question
Ok another question if you don't mind. I have an output transformer that has 4/8/16 ohm tap. Can I just connect the feedback circuit to the 16 ohm tap or do I have to have the feedback connected to whatever tap I'm using at the time?
Mullard 3-3. Three Watt Amplifier
Ok another question if you don't mind. I have an output transformer that has 4/8/16 ohm tap. Can I just connect the feedback circuit to the 16 ohm tap or do I have to have the feedback connected to whatever tap I'm using at the time?
Mullard 3-3. Three Watt Amplifier
You can connect NFB to the 16 ohm tap, but you would have to adjust the NFB voltage divider resistors accordingly.
I would forget about the Mullard 3-3, it is a very poor and outdated design.
I would forget about the Mullard 3-3, it is a very poor and outdated design.
I'm told not to try building this amp and then I hear Crickets? If this is a bad design what's a good one?
Any help would greatly be appreciated, As it's a lot of work putting amps together. Thank you very much in advance.
I did the Mullard 520 before and it's a great sounding pair of monoblocks. That's why I trusted this circuit would work.
Any help would greatly be appreciated, As it's a lot of work putting amps together. Thank you very much in advance.
I did the Mullard 520 before and it's a great sounding pair of monoblocks. That's why I trusted this circuit would work.
This is one of two that I'm starting with. They still need punched and painted.
An externally hosted image should be here but it was not working when we last tested it.
Go ahead and build it, looks like fun.
It would make a good little amp for listening to talk radio, or even a television amp.
(Not home theater obviously.)
It would make a good little amp for listening to talk radio, or even a television amp.
(Not home theater obviously.)
Worth a shot I'd say. I did an all pentode 6J7 / 6V6 design a few years back and has proved quite satisfactory.. Some of my friends even like it.. 😛
I don't see anything glaringly wrong with that design. In fact, I commend Mullard for documenting it so well. I would build it without the tone controls.
The topology is pretty fool-proof and opens up a lot of options if you're into modifications. With 100 mV sensitivity, you could definitely increase the amount of feedback (watch for stability issues), lower the gain, and lower the THD. You could also try a triode driver rather than the EF86 pentode, though the EF86 is supposed to be quite excellent. You could also try some plate-to-plate (Schade) feedback. If your OPT supports it, you could try ultra-linear operation. Options, options...
Looks like a fun project. With 3 W, you're not going to rock your house off its foundation but with reasonably efficient speakers, it'll be plenty loud under most circumstances.
~Tom
The topology is pretty fool-proof and opens up a lot of options if you're into modifications. With 100 mV sensitivity, you could definitely increase the amount of feedback (watch for stability issues), lower the gain, and lower the THD. You could also try a triode driver rather than the EF86 pentode, though the EF86 is supposed to be quite excellent. You could also try some plate-to-plate (Schade) feedback. If your OPT supports it, you could try ultra-linear operation. Options, options...
Looks like a fun project. With 3 W, you're not going to rock your house off its foundation but with reasonably efficient speakers, it'll be plenty loud under most circumstances.
~Tom
Yeah I didn't have any plans of putting it together with tone controls. And as seen in my pic, My outputs don't have an ultra linear tap. From what I've heard, The 3.3 has plenty of gain. So I'd probably install a volume control
I've seen a few prints out there, But nothing that seemed to be that well documented. If there was a well established 3 watt EL84 SE print out there, I would like to see that before I make my decision.
Right now I have plenty to do, I can punch the chassis, set up inputs, outputs, get sockets/transformers mounted and get the chassis and cans painted.
I've seen a few prints out there, But nothing that seemed to be that well documented. If there was a well established 3 watt EL84 SE print out there, I would like to see that before I make my decision.
Right now I have plenty to do, I can punch the chassis, set up inputs, outputs, get sockets/transformers mounted and get the chassis and cans painted.
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