These were well under $200 ea a couple years ago.Probably $250 to $300 today. They were 3.5W UL output using 6P1P-EV and low end Edcor Iron. I believe they were actually better than the iron in the Magnavox amps I have worked with.
CSXE are $42 ea, Power is just over 100, so 250 is probably reasonable for someone who is resourceful.
Build Thread - Firefly
CSXE are $42 ea, Power is just over 100, so 250 is probably reasonable for someone who is resourceful.
Build Thread - Firefly
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The $50 stereo Magnavox is not a substandard sounding amp. Using K40Y-9 Russian coupling capacitors, a JJ E83CC and Mullard EZ-81 rectifier the sound is outstanding. This is the amp that started Bottlehead SE 6BQ5 design as he was impressed with this Magnavox.
You may well turn out to be correct however...
Tired of building larger more complex expensive amplifiers for a break I am in the process of designing and building a small 6F5P PP based amplifier that is designed to use off the shelf transformers that should cost under 100USD for a stereo set of output and power transformers.
A 6F5P can drive low impedance loads and this it seems opens a possibility for low cost low power toroids to be used as the output transformer with good results.
Calculation shows the -3dB power point from 15watts will be 33Hz with the low cost transformer I picked.
So not bad over all and pretty good for ultra low cost.
Tests on the transformers suggest leakage inductance and capacitance will be low enough to allow good high frequency performance at the low impedance the 6F5P will be loaded by.
Local feedback within a high gain differential input stage is used to lower the anode impedance of the 6F5P to further mitigate transformer limitations.
Expected power output will be 10~15 watts depending on how complex a power supply (regulated or not) you are willing provide.
Predicted THD distortion at full power is looking to be solidly under 0.5%, not wonderful but pretty good for a entry level low cost project.
Damping is predicted to be 10.5 or better, again not wonderful but pretty good.
Only two tubes will be needed per channel.
Will it be high end audio. No.
It should however if my calculations are close to correct produce a satisfying tube audio HiFi experience for the newcomer without a lot of cash.
If it works out I will post the design in the fall when I get the circuit boards build and tested.
If not I will learn some more in the process of failure. All good fun.
Thinking about this some more there is the "baby huey" design that is a reasonable low design if one dispenses the "high end" resistors and capacitors and goes with standard quality parts.
Search on "EL84 Amp - Baby Huey"
Using the Antec transformer "MP-10W80 10W Audio Output Transformer $44" it may be possible to hit the $200 dollar target.
Search on "EL84 Amp - Baby Huey"
Using the Antec transformer "MP-10W80 10W Audio Output Transformer $44" it may be possible to hit the $200 dollar target.
There is plenty of Grundig single-ended OPTs and power supply modules on eBay, from old tape recorders, usually for EL84/ECL86/82 and the likes, going for £10~15 each. If 3W is enough then an ECL86 SE should be feasible with that budget.
In a tube amplifier... the output transformer is a very important part. Never forget. Radio output transformers are only made for the middle sound. The reason is the small of the core. If you want to have a single 3 + 3 watt. The output transformer should be 800 grams minimum. I bought its material and learned how to winding. most not do this.
5k -----8 -16 ohm. 28 h. for se 12 to 15 watt. only by 20$ matrial.20$ for winding= 40$ .......
I would find it very interesting to learn about how, what and where you source materials and how you wind and with what equipment.
Perhaps a thread on this? If already started could you provide me a link or title?
Thanks.
Check out my post on the “Elekit TU-8100 as a phones amp“.
It’s only 2 wch but sounds great with high efficiency spks and phones with a voltage divider box like I made.
It’s a fun Inexpensive easy kit to assemble. And you may be surprised using it with normal efficiency spks as long as you don’t expect to get loud levels.
It’s only 2 wch but sounds great with high efficiency spks and phones with a voltage divider box like I made.
It’s a fun Inexpensive easy kit to assemble. And you may be surprised using it with normal efficiency spks as long as you don’t expect to get loud levels.
Cheap amps? How about Eli Duttman's El Cheapo design, using 12AQ5 output tubes (basically a 6V6GT in a 7-pin mini bottle with a 12.6V heater), 12AT7 LTP driver, cheap Allied power transformer and whatever output transformers you can find.
The 12AQ5 tubes are still relatively cheap.
12AT7 is the same thing as ECC81. You only need two good ones and they're available from JJ, Sovtek, etc.
You could use an Antek toroid power transformer that would be up to the task.
https://www.antekinc.com/as-1t250-100va-250v-transformer/
$42 (not including tax and shipping) complete with two 6.3V 3A heater windings which could be wired in series to make 12.6V. Or use Russian 6P1P output tubes, which are 6V6GT in a 9 pin mini bottle.
The output transformers are going to be a challenge. You want something like a 6.6k plate-plate primary to 4 and 8 ohms secondary (16 ohms optional). 8k or 10k primary could also be used. 6.6k would give the most output power but at higher distortion. 10k would give the least output power but with better damping and lower distortion. Maybe one of the cheaper Edcor open frame PP OPTs would do, like this one for $58 each: https://edcorusa.com/products/xpp25...utput-transformer?_pos=4&_fid=ce4e8f6f0&_ss=c
For the filter choke, you could use an Antek 3H 250mA part $42 - https://www.antekinc.com/lk-3h250-toroidal-power-choke/
or an Edcor 2H 200mA choke for $34.50 - https://edcorusa.com/products/xc75-2h-200ma-2h-200ma-choke
The rest will add up, of course.
The other problem will be that this would not be a kit with a PCB for you to stuff, etc. You'd have to create the parts layout and hand-wire it point-to-point. It's a lot of work. Make sure you use a nice, big chassis and leave yourself plenty of space.
Another possibility would be Tubelab's Simple Push Pull (SPP) design. http://tubelab.com/designs/tubelab-spp/
There might still be PCBs available. The project has good documentation and a builder's guide.
I'd use Russian 6P14P in that (substitute for EL84) or the JJ EL84 (more expensive). Same transformers as above.
A scrounged Magnavox would also work out, but you'd be best off scrounging around Craigslist rather than eBay. Magnavox console amps are no longer a sleeper/secret.
I hope you get a usable pair of OPTs out of that Facebook ad purchase.
The 12AQ5 tubes are still relatively cheap.
12AT7 is the same thing as ECC81. You only need two good ones and they're available from JJ, Sovtek, etc.
You could use an Antek toroid power transformer that would be up to the task.
https://www.antekinc.com/as-1t250-100va-250v-transformer/
$42 (not including tax and shipping) complete with two 6.3V 3A heater windings which could be wired in series to make 12.6V. Or use Russian 6P1P output tubes, which are 6V6GT in a 9 pin mini bottle.
The output transformers are going to be a challenge. You want something like a 6.6k plate-plate primary to 4 and 8 ohms secondary (16 ohms optional). 8k or 10k primary could also be used. 6.6k would give the most output power but at higher distortion. 10k would give the least output power but with better damping and lower distortion. Maybe one of the cheaper Edcor open frame PP OPTs would do, like this one for $58 each: https://edcorusa.com/products/xpp25...utput-transformer?_pos=4&_fid=ce4e8f6f0&_ss=c
For the filter choke, you could use an Antek 3H 250mA part $42 - https://www.antekinc.com/lk-3h250-toroidal-power-choke/
or an Edcor 2H 200mA choke for $34.50 - https://edcorusa.com/products/xc75-2h-200ma-2h-200ma-choke
The rest will add up, of course.
The other problem will be that this would not be a kit with a PCB for you to stuff, etc. You'd have to create the parts layout and hand-wire it point-to-point. It's a lot of work. Make sure you use a nice, big chassis and leave yourself plenty of space.
Another possibility would be Tubelab's Simple Push Pull (SPP) design. http://tubelab.com/designs/tubelab-spp/
There might still be PCBs available. The project has good documentation and a builder's guide.
I'd use Russian 6P14P in that (substitute for EL84) or the JJ EL84 (more expensive). Same transformers as above.
A scrounged Magnavox would also work out, but you'd be best off scrounging around Craigslist rather than eBay. Magnavox console amps are no longer a sleeper/secret.
I hope you get a usable pair of OPTs out of that Facebook ad purchase.
30 years ago, you could pick up unwanted vintage tube integrated amps for cheap. Everybody wanted the best Eico, Fisher, Scott, Harman-Kardon, Dynaco amps, but nobody wanted Bogen, Heathkit (except the Williamson amps), Knight, Lafayette, Pilot, stuff like that. But that has completely changed. I find it hard to believe that this untested Bogen stereo tube amp is going for $245 plus shipping - https://www.ebay.com/itm/276360963418
I'm not sure you'd save any money starting with a not-so-desirable vintage amp if it costs $200+ already.
I'm not sure you'd save any money starting with a not-so-desirable vintage amp if it costs $200+ already.
Caveat Emptor.
Who is going to pay shipping for an old wood console stereo?
Who will enjoy working with a corroded Magnetic Steel chassis?
Etc.
If you want to restore corrosion, wood finishes, replace old capacitors, that is what you want to do.
If you want to build from all new parts, that is another thing.
You get what you pay for.
"Cheap is not good, and good is not cheap" Frank Reps . . . Sound Practices . . . Baby Ongaku 2A3 single ended
All generalizations have exceptions
Who is going to pay shipping for an old wood console stereo?
Who will enjoy working with a corroded Magnetic Steel chassis?
Etc.
If you want to restore corrosion, wood finishes, replace old capacitors, that is what you want to do.
If you want to build from all new parts, that is another thing.
You get what you pay for.
"Cheap is not good, and good is not cheap" Frank Reps . . . Sound Practices . . . Baby Ongaku 2A3 single ended
All generalizations have exceptions