DIY tube amp plans??

[cinema bob]

Hi guys I know that this area is mostly for speakers but i have seen some amp discussions in here before so I thought id give it a go. I was wondering if anyone had or knew where i could find some plans or (preferably) layout for a KT88 and 12ax7 tube monoblock amp? kinda like a mono version of the consonance ella but mono. The reason I really want those tubes is I have a small stockpile of used but good Mullard, telefunken and "fender by RCA" tubes and want to build an amp around them.

anything around 30-50 watts would be cool... well anything would be cool really but that would be ideal.

[Geoff Gunnell]

Have you enquired in diyaudio's tube section and audioasylum's diy tube section?

[Hdale85]

Check out the tube cad journal as well just google it. Tons and tons and tons of pages to read. Also read this.

http://boozhoundlabs.com/howto/ this will help you get started with building your own design.

[cinema bob]

thanks guys, I really appreciate it.

[Arc00]

http://www.s5electronics.com/

[A9X]

First of all, ditch the 12AX7 idea, it's junk. There are much better tubes and combinations out there.

[cinema bob]

um, no. I want to use a 12ax7. If you dont like it then cool but i do.

[joetama]

First of all, ditch the 12AX7 idea, it's junk. There are much better tubes and combinations out there.

Just curious of what a better combination would be.

[knifeinthesink]

somewhere on the diyaudio website (you'll have to search, i haven't been there in a long time) there is a post where people list their favorite amplifier designs. I think there are tube designs mentioned. I found it quite interesting.

[A9X]

um, no. I want to use a 12ax7. If you dont like it then cool but i do.

Go ahead then. It's the least linear tube I've ever tried in any variation, and it seems a waste to make a decent amp and cripple it with such a crummy tube. GNFB will help, but it's a case of silk purses and sows ears. It also have no drive capability to speak of.

Before you randomly build a tube amp, invest in Morgan Jones' Valve Amplifiers.

Just curious of what a better combination would be.

How much gain do you want, and what sort of load will you need to drive? The generic 12AX7 common cathode stage will give about a gain of 60 and an output Z of 38k with a bypassed cathode. A CCS loaded 6N1P will give 6dB less gain, but much lower distortion and about 8k O/P Z. This is the first OTTOMH pick for transplaning into a design with a 12AX7, but there are lots of other factors that I would need to consider in a real world design.

Best amp design I've tried recently is SY's Red Light District, for about 17W PP pentode. Search diyaudio for it. Parallel the O/P tubes for double the power. My friend built one and I was very impressed with it and he is going to add another pair of EL84's when he gets the chance as he could do with a bit more power.

My own preferences revolve around zero NFB class A PP designs, though I'm currently building Pass deigns for my music/HT system.

[Amphiprion]

Please be very careful with the voltages involved in tube amplifiers. 500V isn't too bad in the grand scheme of things, but make sure your wiring insulation is rated well above your B+, place bleeders on all caps, and read up on high voltage safety.

Like I said, 500V isn't too hard to be safe around, but it's getting close to the range where currents can arc through wiring insulation, test probe leads, etc. I had a 1KVrms LCD backlight inverter arc through a lead on a DMM probe because the insulation on the probes wasn't rated for those voltages.

[JRT]

Hi guys I know that this area is mostly for speakers but i have seen some amp discussions in here before so I thought id give it a go. I was wondering if anyone had or knew where i could find some plans or (preferably) layout for a KT88 and 12ax7 tube monoblock amp? kinda like a mono version of the consonance ella but mono. The reason I really want those tubes is I have a small stockpile of used but good Mullard, telefunken and "fender by RCA" tubes and want to build around them.

anything around 30-50 watts would be cool... well anything would be cool really but that would be ideal.

Menno Vanderveen designed a family of tube amps that might interest you.
...described in his book:

http://www.plitron.com/audio_books.asp

The variant that used the Plitron PAT 4006 was designed to use a quad of KT88 or 6550 output valves, ultralinear topology, 100W into 5_Ohms.

Note the wide bandwidth:
-0.1_dB 1.4_Hz to 96.5_kHz
-3_dB at 20.7_Hz at full power

http://www.plitron.com/audio_4006.asp

Plitron offers the output and power transformers, as well as printed wiring boards and enclosures for those.

[JRT]

Go ahead then. It's the least linear tube I've ever tried in any variation, and it seems a waste to make a decent amp and cripple it with such a crummy tube. GNFB will help, but it's a case of silk purses and sows ears. It also have no drive capability to speak of.

Before you randomly build a tube amp, invest in Morgan Jones' Valve Amplifiers.

How much gain do you want, and what sort of load will you need to drive? The generic 12AX7 common cathode stage will give about a gain of 60 and an output Z of 38k with a bypassed cathode. A CCS loaded 6N1P will give 6dB less gain, but much lower distortion and about 8k O/P Z. This is the first OTTOMH pick for transplaning into a design with a 12AX7, but there are lots of other factors that I would need to consider in a real world design.

Best amp design I've tried recently is SY's Red Light District, for about 17W PP pentode. Search diyaudio for it. Parallel the O/P tubes for double the power. My friend built one and I was very impressed with it and he is going to add another pair of EL84's when he gets the chance as he could do with a bit more power.

My own preferences revolve around zero NFB class A PP designs, though I'm currently building Pass deigns for my music/HT system.

Have you tried or looked at Cyrus Brenneman's 6N1P / SV83 base mu stage that was the subject of Svetlana's tech bulletin no.27 (still available in the Internet archive, copied/pasted below)?



Numerous mu-follower and SRPP designs have been presented to the readers of audiophile magazines in recent years. And yet, in spite of the limitations on present-day receiving tube manufacturing, a large proportion of these designs have used tube types which are no longer in production. Such designs are not useful to the OEM of audio equipment, as he cannot be guaranteed of future supplies of the tubes for his product line.

The mu-follower presented here uses only Russian-made tubes of current manufacture. Its performance and sound are the equal of nearly any other mu-follower yet presented to the public or used in a commercial design. Thanks to the high transconductance and high linearity of the SV83 and the very high linearity of the 6N1P, distortion is vanishingly low at line levels, making this circuit excellent for no-feedback preamp line stages. And the large cathodes of the 6N1P offer superior performance and lifetime to 6922-type dual triodes.

This circuit, when operated on the full 500-volt plate supply shown, can drive a single SV572-3 effectively. If the SV572-3 is operated on its maximum 1000-volt supply, the resulting power output is in excess of 25 watts in Class A2. Other power tubes, such as the 300B, 211 or 845, are also suitable for use in SE designs using this mu-follower as a driver. In any case, it is recommended that the resistors and capacitors in this circuit be audiophile grade. Coupling capacitors should be polypropylene or PTFE dielectric. The 100k input resistor may be replaced with a 100k volume control if desired. The heaters of the SV83 and 6N1P may be operated on AC or DC, the latter being recommended for best noise performance in a line stage. Because the cathode of the SV83 is about 250v dc above ground, two methods of powering the heaters are recommended. One way would be to use separate supplies, one at ground potential for the 6N1P. The SV83 supply may then be stood above ground with a resistive divider attached to the 500v plate supply and then to either end of the heater, or to a center-tap in the filament winding of the power transformer. A simpler and well-tested method would be to use a single supply to power both the 6N1P and the SV83, floating completely free from the rest of the circuit except for a capacitor to suppress induced noise. This capacitor may have to be selected experimentally in a breadboard, for best noise suppression. Start with 0.22 uF, 600v, polyester dielectric. For best lifetime of the tubes in this circuit, a delay in the plate supply is recommended. A standby switch or a slow-warmup rectifier tube (such as the Svetlana 6D22S) are suitable methods of obtaining this delay. An electronic delay relay may also serve this purpose, with the delay set for at least 15 seconds to allow proper warmup of the 6N1P and SV83.

OBSERVED PERFORMANCE (measured on breadboarded prototype)

---------------------------------

Voltage gain at 1000 Hz:

about 30

Frequency response:

<10 Hz to >50 kHz, -1 dB

Maximum output signal into 47k-ohm load, at 1000 Hz, onset of clipping:

125v RMS (354 v p-p).

Distortion into 47k-ohm load at 1000 Hz:

0.08% at 10 v RMS out

0.45% at 100v RMS out

[A9X]

Have you tried or looked at Cyrus Brenneman's 6N1P / SV83 base mu stage that was the subject of Svetlana's tech bulletin no.27 (still available in the Internet archive, copied/pasted below)?
........

OBSERVED PERFORMANCE (measured on breadboarded prototype)

---------------------------------

Voltage gain at 1000 Hz:

about 30

Frequency response:

<10 Hz to >50 kHz, -1 dB

Maximum output signal into 47k-ohm load, at 1000 Hz, onset of clipping:

125v RMS (354 v p-p).

Distortion into 47k-ohm load at 1000 Hz:

0.08% at 10 v RMS out

0.45% at 100v RMS out

Yes, I saw it years back. I use cascoded MOSFETs or IXYS CCS for ease, lower B+ and even better performance.

The measured specs look pretty good and are way better then a 12AX7 can do.

Another alternative is to use a 12HG7 or 12GN7 in pentode mode, but they do draw a lot of current. Cascoded 6DJ8 or 6H30 also give lots of gain, low distortion and reasonably low O/P Z but ultimate performance is PS limited, ie PS must be good as PSRR of the stage is very low.

Morgan Jones also has a 6SN7 based Beta-follower in VA: perhaps a 6N1P version would also work well. I haven't tried it, just throwing around ideas.

[fjhuerta]

Go ahead then. It's the least linear tube I've ever tried in any variation, and it seems a waste to make a decent amp and cripple it with such a crummy tube. GNFB will help, but it's a case of silk purses and sows ears. It also have no drive capability to speak of.

Since the point of a tube amp is euphonic distortion, then wouldn't a 12AX7 be a matter of taste?

[A9X]

Since the point of a tube amp is euphonic distortion, then wouldn't a 12AX7 be a matter of taste?

Depends on how you define euphonic as well as what you're trying to achieve by building the amp. I generally don't want to know of the amplifier's presence by a particular sonic signature, especially one that has a distortion that is not monotonic. Tube amps do not have to be obvious (audible) distorters unless you choose to design them that way.

The most revered small signal tube is the 6SN7 and the power tube is often the 300B, 2A3, 45, 845 etc. These are some of the most linear devices ever made.

[JRT]

Depends on how you define euphonic as well as what you're trying to achieve by building the amp. I generally don't want to know of the amplifier's presence by a particular sonic signature, especially one that has a distortion that is not monotonic. Tube amps do not have to be obvious (audible) distorters unless you choose to design them that way.

The most revered small signal tube is the 6SN7 and the power tube is often the 300B, 2A3, 45, 845 etc. These are some of the most linear devices ever made.

A screen driven (enhanced triode) EL509 is also no slouch when it comes to linearity.

http://www.svetlana-mvsz.com/Svetlana%20EL509.pdf

[A9X]

A screen driven (enhanced triode) EL509 is also no slouch when it comes to linearity.

http://www.svetlana-mvsz.com/Svetlana%20EL509.pdf

I have the tubes, but never got around to screen drive. Maybe one day.....

[JoshK]

I'd say to take a look at the classics for a place to start thinking. Like the Mullard circuit and think about modernizing it with some CCS's in the differential driver, etc. 6SN7's or 6N1P, or any other linear tube is better than using a non-linear tube and fixing it with gNFB. I like the front end in Morgan Jone's Crystal Palace.

[JRT]

I have the tubes, but never got around to screen drive. Maybe one day.....

With EL509's nominal 18,000 microsecond transconductance, might be good in the role of screen driven cathode follower.

http://www.svetlana-mvsz.com/Svetlana%20EL509.pdf

There are some variants of the EL509 that do away with the anode cap and use an octal base, such as this one:

http://lib.store.yahoo.net/lib/thetubestore/JJ-EL509-S.pdf

[castlesteve]

KT88 amp

Hi guys I know that this area is mostly for speakers but i have seen some amp discussions in here before so I thought id give it a go. I was wondering if anyone had or knew where i could find some plans or (preferably) layout for a KT88 and 12ax7 tube monoblock amp? kinda like a mono version of the consonance ella but mono. The reason I really want those tubes is I have a small stockpile of used but good Mullard, telefunken and "fender by RCA" tubes and want to build an amp around them.

anything around 30-50 watts would be cool... well anything would be cool really but that would be ideal.

This is a 9-10 watt amp but sounds really nice.

http://www.diyaudio.com/forums/attachment.php?s=&postid=671676&stamp=1119993206

http://img.villagephotos.com/p/2007-...0-Audio003.jpg

If you want more power then you could try this:http://www.plitron.com/vtvkt88.asp
Good luck, Steve.