Nice amp! Can you please upload amp and PSU schematics?

hello costas,
please can you send me to my email final tuned schematic and PSU plus bill od materials ( may be in eagle format )for this tube amp with 6L6? I want build some easy tube amplifier.
my email is: (e-mail hidden for security reasons )
many thanks
milan

I'm also very interested in seeing the power supply.

I've been wanting to do a 6L6 amp as winter project and this may fit the bill. I've got Edcor 5K single-ended OPT's and a Stancor PC-8405, 120ma 270-0-270 Ac @120v Rectification at 5.0v a 3.0amp, 6.3 CT at 3.5a power brick.

Have any idea if this transformer would fit the bill.

Also is the schematic designed around a 50hz or 60hz mains power.

Thanks,

Marty

Costas, Thanks for putting that up. It really is a simple sweet looking design, just what I may need since instead of simply restoring equipment I'm finally trying to build something from scratch. My goal is to have a better understanding of how the squiggles on a schematic convert into the reality of wiring etc.

Any chance I could substitute a 6CG7 instead of that 6FQ7A?

Also, are you part of the Athens stereo crowd that includes my good friend from the Klipsch Forum, the crazy Brit, MaxG?

Marty

Beautiful part of your country. I remember it fondly although it's been 30 years since I've been there.

Yes, that's the crowd my online friend Max runs with.

Thanks for your prompt response and I'll await the final schematics.

Marty

The final modified schematic is available. I posted in the main article. The changes concern the R4 (350 ohms) and the direct voltage (240 V) from the PSU to pin 4. We applied no feedback at all.

costas

hello costas,
plase could you make measure for square and sine wave 10 and 20kHz to 1W output power.
thanx
milan

Milan I have in mind to perform a measurement again may be at the end of this month, because I m too busy at the moment. When I will perform it I will post some photos.

costas

Looks very nice, with a simple parts list using widely available values. Pretty cool.

Excuse my ignorance, though, I do have a couple of questions.

Is the variable resistor rated at 250K or is that your volume pot. Is that a two gang volume pot, and if different, what's it's rating?

Not familiar with the symbol for the value on R7 and R5 could you edify?

Again, excuse my ignorance but are C2 and C3 on the modified schematic the 300uf ceramics shown on the power supply?

Finally, how's it sound? (smily)

Well , actually the 250K works as a volume pot. As you can see it, this is a three stage amp with the first stage (voltage amp stage ECC83) works like a pre-amp. Furthermore the two resistors R5 and R7 in series have total resistance value of 230K. This is for dropping 75 Volts in the plate of the ECC83. Christos put 2 resistors in series, but you can use only one resistor 230K for dropping the 75 Volts, or you can change it according to your taste if you decide to change the plate voltage of the ECC83. For this reason named X. The two capacitors C2 ,C3 are for extra filtering. Just ignore them.
About my listening impressions I have to say that this pretty amp sounds sweet with good performance on one condition : It should drive horn type loudspeakers. Under this condition it can reproduce a clean and wide sound stage.

costas

PS ( sorry for the delayed answer - I m too busy these days - and as you can understand this is not my profession, it is my hobby ;-) )

Well I've got the various parts in, the case is built and I'm ready to proceed. Since these will be run through very high efficiency speakers (Klpsch Cornwalls and/or Heresy's) Im sure the amp will sound just fine.

One additional question, though. Was their any particular reasoning behind modifying the schematic? I ask because I'm not sure what version to build.

Appreciate your assistance, and no need to rush on your response.

Marty

Oh, and I'll send along pictures and post comments once it's built and playing.

Well I've bult it but I'm running into problems. The cathode voltage on the 6L6's keeps rising.

First I have made a couple of changes. I've added a fuse, pilot light and on/off switch on the AC side and added a 3 wire American-style safety cord for wall power. I'm using a 270-0-270 120ma power transformer, 6.3 volt on heaters, a center tap on the primaries and 5v lines for the rectifier. I'm using a 5U4GB for rectification and becuse of this I have changed the four 47uf/250v can values to two 40uf/450v. I have also tried it with twin diodes still using the center tap. I'm using a 5K gain pots, 230K resistors for R7 and R5 and 5K/8ohm Single-ended output transformers. I'm using 350ohm 3watt resistors at the cathode. I'm using a big Hamond 2.6henry 300ma choke and have also substituted 300ohm and 500ohm 10watt resistors in place of the choke.

I do have speakers hooked up and am using a 1K 1/2 wtt resistor loads at the inputs

What is happening is that the cathode voltages keep rising, and as they do they lower the voltage readings at all four power caps. My friend figures the voltage should be about 14 to 20 volts, but the power curve never levels off and I usually shut it down at about 40 volts after those 350ohm 3 watt resistors start getting very hot.

I started out with both channels built. In that configuration both 6L6's would start out at the same voltage but eventually one would continue to rise and the other would fall of to nothing. So I stripped out one whole channel but still get the rising voltage.

I've used a variety of 6L6's inclduing Jan spec 6L6GB's which are very rugged tubes so I don't think it's the tubes.

At this point about all I can think is that somehow my power transformer can't handle this, but I sure would be open to any suggestions.

Thanks,

Marty

I Think, Never Mind

I added a standby switch to let the heaters warm up first.

At the same time, I made a slight change to the heater wiring at the 12AX7. I had pins 4 and 5 tied together to get the 6.3 ac but instead of leading off to the next tube from Pin4 where the ac originally line came in, I was leading off from Pin 5. I have no idea if that change affects things at all. Probably not.

Now after letting the tubes warm up for a few minutes I turned on the standby switch. The voltage shot right up but after a minute or so it started to slow down and while still climbing ever so slightly it seems to have steadied down at around 39 volts.

By the way I did put in a 10k to ground resistor for the last cap which was showing a voltage of around 200 and that dropped it dramatically. but now it's too low showing only about 90volts with the cathod reading around 39. It seems I will have to tweak power supply resistors and maybe cathod resistors. Not to mention rebuilding the second channel and hoping everything falls into place.

Still any thoughts, advice are appreciated.

Thanks ! We will upload all schematics (amp & PSU) and data curves also, until the end of this week. stay tuned !

Sorry If I missed it in the postings, wht is the typical output power.

Thanks,

Excellent .... I am looking for a project like this for myself and my son.

Looking forward to any information that follows such as full schematic, Transformer specs and if possible layout and sound samples.....

Great job........

Hi Costas,
I noticed, you employed two 47uF/250V Cap's in series configuration in your power supply. I recommend you to connect 100K resistor parallel to each capacitor. As it is, standing voltage across the series capacitors are divided arbitrarily depends on the leakage (equivalent internal resistance) of the each capacitor. By adding these resistors you may help to divide the voltage equally between the two capacitors. When ambient temperature icreases, leakeges icreases (equivalent internal resistor decreses) so 100K may not be sufficient for the purpose and you may use 50K instead; naturally,in this case you burn more power on the resistors.
Regards,
Kazim.

Hi, was looking for an easy starter project for tubes (have a lot of experience with little chip-based amplifiers and pretty used to point-to-point wiring), so thanks for sharing. Very quickly, will the 12AX7 work for VA/VA2? I have access to some RCA 6L6, and those might fit right into the project, though I'm unsure of the OPT, don't know wher I can get one from - I'm in India.

Sorry, I also missed the values of R5 and R7, they seem to be missing from the latest schematic...