It's the transformers that make any valve amplifier. Schematics are great but I have not yet seen one that includes detaios of what transformers to use to obtain the quoted results.
Electra-Print sell some outstanding transformers, complete with schematics at outstanding prices. Has anyone actually built one of their designs ?
Audio-Note also provide some oustanding kits but their prices are ENORMOUS - £1500 for a DIY amplifier - Out of my league I'm afraid.
Electra-Print sell some outstanding transformers, complete with schematics at outstanding prices. Has anyone actually built one of their designs ?
Audio-Note also provide some oustanding kits but their prices are ENORMOUS - £1500 for a DIY amplifier - Out of my league I'm afraid.
Just to make things more interesting, I recently purchased a Magnavox 93-04-20 6BQ5/EL84 P-P console amp through eBay for less than $100. For about $50 to $75 more in new resistors, new coupling caps, new electrolytic caps and other parts, I think I'll have a nice little power amp to drive my Klipsch Forte IIs.
I just received it last week, and used some Nevr-Dull polish to shine up the plated steel chassis. This little guy came with the original Magnavox labelled Mullard 6BQ5 power tubes, Mullard 6EU7 driver tubes and a Tung-Sol 5U4GB. I'm going to build a finished wood frame to wrap around the steel chassis, add an IEC inlet, fuse and power switch, and replace the speaker tag strip with binding posts.
A great resource for upgrading and restoring these console amps is the Yahoo! Group "Magnavoxfriends" (Magnavoxfriends : Magnavox Friends). The output trannies aren't world beaters, but they'll do well with efficient speakers like the Forte IIs. Some people have restored the Magnavox 6BQ5 single ended pentode console amps or modified them to the RH84 SE amp circuit with very good results.
Consider these to be almost like half-kits on a tight budget. I'm willing to bet that this P-P amp will sound better than my other budget EL84 amp from Suppo. I think I'll name the amp "Ugly Betty."
I just received it last week, and used some Nevr-Dull polish to shine up the plated steel chassis. This little guy came with the original Magnavox labelled Mullard 6BQ5 power tubes, Mullard 6EU7 driver tubes and a Tung-Sol 5U4GB. I'm going to build a finished wood frame to wrap around the steel chassis, add an IEC inlet, fuse and power switch, and replace the speaker tag strip with binding posts.
A great resource for upgrading and restoring these console amps is the Yahoo! Group "Magnavoxfriends" (Magnavoxfriends : Magnavox Friends). The output trannies aren't world beaters, but they'll do well with efficient speakers like the Forte IIs. Some people have restored the Magnavox 6BQ5 single ended pentode console amps or modified them to the RH84 SE amp circuit with very good results.
Consider these to be almost like half-kits on a tight budget. I'm willing to bet that this P-P amp will sound better than my other budget EL84 amp from Suppo. I think I'll name the amp "Ugly Betty."
Rare to see a console amp with a choke.
My stereo RH84 has Magnavox OPTs (a grundig power trafo, and a choke from a hammond organ)
dave
It's pretty common to see the older consoles with field coil speakers, using the field coil for power supply filtering. Does that count?
I call my Magnavox 93-04-20 console amp "Ugly Betty," because it is kind of ugly. Anyway, I hooked it up to the variac and to a pair of cheapie Kenwood mini system speakers. For a source, I used a Sony Discman with it's output level control. This amp must be in good shape, because I could only hear a faint hum only when the music wasn't playing, and I had my ears right up to the speakers. So far, I've only jumpered the power tranformer primary wires so I could power up the amp with a variac, and installed two 390 ohm resistors to replace the absent 750 ohm balance pot.
http://www.audiokarma.org/forums/attachment.php?attachmentid=219641&d=1278821893
Next, I'll install new coupling caps, new Silver Mica caps in the feedback loop and a CE Manufacturing multi-section can cap (80uF/40uF/30uF/20uF @ 475V). I'm using the 40uF section right after the 5U4GB rectifier tube, the 80uF section right after the choke, the 30uF section right after the 22k power resistor, and the 20uF for the cathode bypass. The CE Manufacturing can cap is exactly the same size as the stock can cap. I'm also installing an IEC inlet, fuse, power switch and new binding posts.
http://www.audiokarma.org/forums/attachment.php?attachmentid=219642&d=1278821893
Even with these cheap little Kenwood speakers, I was amazed at the soundstage and controlled bass. It defintely had a nice warm sound, and I may hold off on replacing the stock Carbon composition resistors for now. Most of them measured okay considering their age. I bought a bunch of replacement 1/2 watt Carbon film resistors from Mouser just in case. All the stock Mullard 6EU7 and Mullard 6BQ5 tubes tested strong. The Tung Sol 5U4GB tested good, but it might be getting close to the end of its life. Anyway, I can't wait until my rebuild is completed, so I can hook them up to my Klipsch Forte II speakers. Ugly Betty might turn out to be a beauty after all.
http://www.audiokarma.org/forums/attachment.php?attachmentid=219641&d=1278821893
Next, I'll install new coupling caps, new Silver Mica caps in the feedback loop and a CE Manufacturing multi-section can cap (80uF/40uF/30uF/20uF @ 475V). I'm using the 40uF section right after the 5U4GB rectifier tube, the 80uF section right after the choke, the 30uF section right after the 22k power resistor, and the 20uF for the cathode bypass. The CE Manufacturing can cap is exactly the same size as the stock can cap. I'm also installing an IEC inlet, fuse, power switch and new binding posts.
http://www.audiokarma.org/forums/attachment.php?attachmentid=219642&d=1278821893
Even with these cheap little Kenwood speakers, I was amazed at the soundstage and controlled bass. It defintely had a nice warm sound, and I may hold off on replacing the stock Carbon composition resistors for now. Most of them measured okay considering their age. I bought a bunch of replacement 1/2 watt Carbon film resistors from Mouser just in case. All the stock Mullard 6EU7 and Mullard 6BQ5 tubes tested strong. The Tung Sol 5U4GB tested good, but it might be getting close to the end of its life. Anyway, I can't wait until my rebuild is completed, so I can hook them up to my Klipsch Forte II speakers. Ugly Betty might turn out to be a beauty after all.
Very nice find, you've done well, looks great rhing. I'm jealous 
Looks like easy access to try different circuits down the track if you get the desire, Red Light District, Simple P-P (tubelab), or El Cheapo (but you'll need 7-pin sockets for 6AQ5, unless you use Russian 6P1P). I didn't mention Baby Huey as it needs UL taps on the OPT's. I wonder how long this amp will remain standard?
Looks like easy access to try different circuits down the track if you get the desire, Red Light District, Simple P-P (tubelab), or El Cheapo (but you'll need 7-pin sockets for 6AQ5, unless you use Russian 6P1P). I didn't mention Baby Huey as it needs UL taps on the OPT's. I wonder how long this amp will remain standard?
I'll keep Ugly Betty in the original paraphase splitter circuit form. I bought the amp for less than $100 off eBay figuring the Mullard tubes were a good deal in themselves. I really like the Suppo Golden Voice 1 that I bought and tweaked too, but I wanted to try the Magnavox, since I read that the paraphase splitter topology tends to retain second harmonics. I think this amp will end up sounding better than the Suppo amp. The point-to-point wiring is a lot easier to work with too. In the U.S., one can still find a good deal on a Magnavox console amp for less than $100.
I bought George's Tubelab Simple P-P board too, and I will build that later this year when I can save enough money to buy Magnequest MQ-575 OPTs with Nickel stripes. I've heard Simple SE amps with good iron and they were very impressive. I wouldn't expect anything different from the Simple P-P when using high quality OPTs. I guess you can tell I have an affinity for 6BQ5/EL84 amps.
I bought George's Tubelab Simple P-P board too, and I will build that later this year when I can save enough money to buy Magnequest MQ-575 OPTs with Nickel stripes. I've heard Simple SE amps with good iron and they were very impressive. I wouldn't expect anything different from the Simple P-P when using high quality OPTs. I guess you can tell I have an affinity for 6BQ5/EL84 amps.
On the topic question, best kit
for EU members, this World Design kit looks like good value
Even available with relay input option
World Designs Amplifier Kits
for EU members, this World Design kit looks like good value
Even available with relay input option
World Designs Amplifier Kits
Update on Magnavox 6BQ5 Amp
After I returned from my vacation, I was able to complete the renovation of Ugly Betty, my Magnavox 93-04-20 6BQ5 console amp. Basically, I made the following changes:
Anyway, I've been listening to this amp with a modified JVC XL-Z1050 CD player with a variable output feeding directly into Ugly betty and then into my modified Klipsch Forte IIs. I was concerned this amp with their little 4ohm OPTs might not have enough bass extension and dynamic slam, but this little amp has no problems driving the Klipsch speakers.
It's still too soon to draw complete comparisons to my upgraded Suppo amp, but I think this amp is smoother in the upper mids and highs. It might also be a bit more extended in the highs, but not in a bright way. The amps sound more similar than different. Overall, I am very pleased with this amp. For the $200 I spent for the amp and parts from Antique Electronic Supply, Mouser and Digi-Key, this was a great bargain in my mind.
After I returned from my vacation, I was able to complete the renovation of Ugly Betty, my Magnavox 93-04-20 6BQ5 console amp. Basically, I made the following changes:
- Replaced .047uF coupling caps to .047uF Auricaps MKP caps and .0015uF coupling caps to .0047 Illinois Capacitor MPW MKP caps.
- Replaced 100pF Mica feedback caps to 100pF Silver Mica caps.
- Replaced multi-section 40uF/30uF/20uF/10uF can cap with CE Manufacturing 80uF/40uF/30uF/20uF can cap (40uF section after 5U4 rectifier, 80uF after choke)
- Replaced most Carbon composition resistors to 1/2 watt Carbon film resistors.
- Replaced 100R/5W wirewound ceramic cathode resistor with Mills 100R/5W wirewound resistor.
- Replaced 10k Carbon composition resistor in power supply with Panasonic 22k/3W metal oxide resistor.
- Installed IEC fused inlet
- Installed Pomona 3770 5-way binding posts
- Installed Radio Shack SPST on/off rocker switch
Anyway, I've been listening to this amp with a modified JVC XL-Z1050 CD player with a variable output feeding directly into Ugly betty and then into my modified Klipsch Forte IIs. I was concerned this amp with their little 4ohm OPTs might not have enough bass extension and dynamic slam, but this little amp has no problems driving the Klipsch speakers.
It's still too soon to draw complete comparisons to my upgraded Suppo amp, but I think this amp is smoother in the upper mids and highs. It might also be a bit more extended in the highs, but not in a bright way. The amps sound more similar than different. Overall, I am very pleased with this amp. For the $200 I spent for the amp and parts from Antique Electronic Supply, Mouser and Digi-Key, this was a great bargain in my mind.
I just disagree with that
The original schemo was developed precisely to void the need of UL taps and be very tolerant about OPT performances !
Yves.
I am building my first P2P amp - an EL84 based on this schematic from John Broskie at Tubecad.com. I am also borrowing a little of what I saw on DIYParadise as far as bias adjustment etc. Its going in a Hammond 12X8X2 chassis and I have ordered all Edcor Iron. Tubes are Sovtek 6N1P and new issue EH EL84's. I am also trying out the Tubecad PS-4 for the PSU. I am using the Tubecad PS-4 for my Aikido preamp and it is flawless.
I just disagree with that
The original schemo was developed precisely to void the need of UL taps and be very tolerant about OPT performances !
Yves.
Yves, I am quite aware of that.
Let me explain. In the Baby Huey thread Gingertubes made it clear that if the amp doesn't run UL then it isn't a "Baby Huey" amp. So my statement is in respect for the author's design. That doesn't stop someone from running a Baby Huey in pentode mode, just don't call it a Baby Huey I guess
I spotted an error on the Broskie schematic - the shared cathode resistor for the EL84s should be 200 ohms, and not 400. Otherwise the EL84s will run about 16.25 mA each, and the sound quality would suffer...
I've built and played around with enough EL84, 6P14P, and 6GK6 designs to know from experience that the tubes like to run at between 30 and 40 mA cathode current, each.
I've built and played around with enough EL84, 6P14P, and 6GK6 designs to know from experience that the tubes like to run at between 30 and 40 mA cathode current, each.
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