Hello, this is my first post here. I've been wanting to get into tube amplifiers for a long while now. I just picked up this vintage tube amp off E-bay and was wondering if anyone could help me identify it. I was told it is from an RCA console and set up for 8ohm speakers. It has two RCA electron tubes marked "6AQ5A". One RCA electron tube marked "12AX7A". One RCA electron tube marked "5Y3GT". It also has some wires sticking out visible in the pics and I have no idea what these are. I want to get this thing sounding good, but I have a long way to go. Any help would be greatly appreciated. Also, does anyone have a good speaker recommendation? I was looking at building some Dayton III speakerbuilder.net.
]Mystery Wires[/URL]
]Mystery Wires 2[/URL]
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The links above do not work. Here are the direct links.
http://img225.imageshack.us/img225/9167/ampsmallao8.jpg
http://img225.imageshack.us/img225/3074/ampinsidessmallhi1.jpg
http://img225.imageshack.us/img225/6240/tubessmallae1.jpg
http://img225.imageshack.us/img225/2513/problem2smalluf8.jpg
http://img225.imageshack.us/img225/7552/problem1smallwm9.jpg
http://img225.imageshack.us/img225/9167/ampsmallao8.jpg
http://img225.imageshack.us/img225/3074/ampinsidessmallhi1.jpg
http://img225.imageshack.us/img225/6240/tubessmallae1.jpg
http://img225.imageshack.us/img225/2513/problem2smalluf8.jpg
http://img225.imageshack.us/img225/7552/problem1smallwm9.jpg
The 6AQ5As are 7 pin pentode power tubes. The 12AX7a is the input stage/voltage amp. The 5Y3GT is the rectifier tube.
First up, before turning it on replace all the capacitors. Those appear to be the originals and are probably leaky/dried/dead. I would also replace the resistors as they have probably drifted quite a bit.
The amp is a single-ended stereo. With the 6AQ5A tubes in pentode mode it might make 4 to 5 watts per channel. In triode mode maybe 1 1/2 watts per channel.
Your choice of speakers depends on the size of your listening room, the distance from the speakers, the type of music you listen to and how loud you'd like it to be. In triode mode you would need very efficient speakers to get very loud with 1.5 watts.
The mystery wires appear to be the wires that went to the speakers in the console, though it would be a good idea to trace out the schematic.
Others with more expertise will undoubtedly be able to offer more info.
First up, before turning it on replace all the capacitors. Those appear to be the originals and are probably leaky/dried/dead. I would also replace the resistors as they have probably drifted quite a bit.
The amp is a single-ended stereo. With the 6AQ5A tubes in pentode mode it might make 4 to 5 watts per channel. In triode mode maybe 1 1/2 watts per channel.
Your choice of speakers depends on the size of your listening room, the distance from the speakers, the type of music you listen to and how loud you'd like it to be. In triode mode you would need very efficient speakers to get very loud with 1.5 watts.
The mystery wires appear to be the wires that went to the speakers in the console, though it would be a good idea to trace out the schematic.
Others with more expertise will undoubtedly be able to offer more info.
Hi mgalvez.
My first suggestion would be to chekout the thread called
online tube learning for newbies. How is you basic electronics knowledge? If you have the basics of dc, ac, ohms law, what capacitors do and so forth, tube amplifiers are quite simple especially a single ended one like yours. checkout sites like
fun with tubes and boozhound labratories.
When I built my first amp, I was concerned that it wouldn't have
enough power to drive my speakers which are rated at 90db
for 1 watt. That amp puts out about 1.2 watts per channel
and is plenty loud, especialy since I have moved into a small
apartment. 90db/watt is fairly average.
Fun With Tubes
boozhoundlabs.com/howto
My first suggestion would be to chekout the thread called
online tube learning for newbies. How is you basic electronics knowledge? If you have the basics of dc, ac, ohms law, what capacitors do and so forth, tube amplifiers are quite simple especially a single ended one like yours. checkout sites like
fun with tubes and boozhound labratories.
When I built my first amp, I was concerned that it wouldn't have
enough power to drive my speakers which are rated at 90db
for 1 watt. That amp puts out about 1.2 watts per channel
and is plenty loud, especialy since I have moved into a small
apartment. 90db/watt is fairly average.
Fun With Tubes
boozhoundlabs.com/howto
Thanks rman, I have a lot to learn. Somebody found the schematic for the amp. Hopefully this will get my project moving foreward.
http://img165.imageshack.us/img165/9252/60rcars182135smallbi1.jpg
So will I be able to hook up a low level input from a source such as a cd player without any modifications? Can I make this amp sound good with speakers such as these?
http://www.speakerbuilder.net/web_files/Projects/D3/dayton3.htm
Thanks again for help.
http://img165.imageshack.us/img165/9252/60rcars182135smallbi1.jpg
So will I be able to hook up a low level input from a source such as a cd player without any modifications? Can I make this amp sound good with speakers such as these?
http://www.speakerbuilder.net/web_files/Projects/D3/dayton3.htm
Thanks again for help.
It is not clear from the diagram what impeadeance speakers
this amp was built for. With tube amps this is important because
the circuit is made for aspecific load. A lower impeadeance load
will get more power but will probably cause the output tube
create quite a bit of distortion. I would sugest to find a very cheap
pair of 8 ohm speakers maybe from a thrift shop just to see if the thing actually works. make sure there is a fuse between the
power plug and the amp before pluging it in. Also make sure
speakers are connected first as well.
It is hard to see from the pictures exactly witch wires connect to
the speakers and the diagram is too small to make out the writing. The two transformers sticking out each end are the output. Trace the wires following the diagram. Each output will
have one wire to a tube and one to the power supply this is the primary side. The speakers connect to the secondary side. You can plug your cd right in to the rca jacks. It might sound quite nice
but I wouldn't expect too much. Just use it as a learning tool.
Have fun but be carfull. do not put your finders inside while it is plugged in or even for a while after you unplug it because the
large capacitor in the power supply can store power for a long time!
Good luck!
this amp was built for. With tube amps this is important because
the circuit is made for aspecific load. A lower impeadeance load
will get more power but will probably cause the output tube
create quite a bit of distortion. I would sugest to find a very cheap
pair of 8 ohm speakers maybe from a thrift shop just to see if the thing actually works. make sure there is a fuse between the
power plug and the amp before pluging it in. Also make sure
speakers are connected first as well.
It is hard to see from the pictures exactly witch wires connect to
the speakers and the diagram is too small to make out the writing. The two transformers sticking out each end are the output. Trace the wires following the diagram. Each output will
have one wire to a tube and one to the power supply this is the primary side. The speakers connect to the secondary side. You can plug your cd right in to the rca jacks. It might sound quite nice
but I wouldn't expect too much. Just use it as a learning tool.
Have fun but be carfull. do not put your finders inside while it is plugged in or even for a while after you unplug it because the
large capacitor in the power supply can store power for a long time!
Good luck!
one more thoght, It looks like this is a dedeicated phono amp for ceramic cartriges. ceramics have a high output so it should work with a cd player... but. It also has a built in equalisation network that strongly boosts the bass and cut the treble because this is needed for playing all vinyl records. maybe if you turn the bass way down and the treble way up it will sound not to bad.
The two resistors and two capacitors just to the left of the loudness control on the diagram form this network. Perhaps
they could be bypased to make this more suitable for cd, tuner,
or other such input.
Cheers
The two resistors and two capacitors just to the left of the loudness control on the diagram form this network. Perhaps
they could be bypased to make this more suitable for cd, tuner,
or other such input.
Cheers
Hi mgalvez.
I doubt that your little amp will ever really be a truly hi-fi amplifier.
Maybe by getting rid of that phono eq network, and puting in a decent pair of output transformers, it might be a decent performer.
If you just want a great sounding very simple power amp and don't need alot of wattage, my best suggestion would be to build
a copy of Gary Kaufman's direct coupled 6em7 amp. You can find
the circuit and pictures of it here.
gary's DC 6EM7
It should work fine with those speakers you are thinking of.
They are 4 omh speakers so you need out put transformers
that will match 5000 omhs to 4 instead of 8. I built one with
Edcore transformers the small single ended ones, and I really
It. It is very simple and the tubes are cheap. You just have to pick good parts and build it carefuly and it will turn out very well.
Good luck.
I doubt that your little amp will ever really be a truly hi-fi amplifier.
Maybe by getting rid of that phono eq network, and puting in a decent pair of output transformers, it might be a decent performer.
If you just want a great sounding very simple power amp and don't need alot of wattage, my best suggestion would be to build
a copy of Gary Kaufman's direct coupled 6em7 amp. You can find
the circuit and pictures of it here.
gary's DC 6EM7
It should work fine with those speakers you are thinking of.
They are 4 omh speakers so you need out put transformers
that will match 5000 omhs to 4 instead of 8. I built one with
Edcore transformers the small single ended ones, and I really
It. It is very simple and the tubes are cheap. You just have to pick good parts and build it carefuly and it will turn out very well.
Good luck.
mgalvez said:
Dude,
A look at the schematic shows that amp to be LOFI, sorry. Pentode mode and no loop NFB is (IMO) BAD. The O/P trafos are quite small, which is indicative of poor bass performance. Passing the AC power cord near an O/P trafo is a NO-NO.
All is not lost.
The 6AQ5 is an EXCELLENT tube (essentially a 6V6 in a 7 pin mini package), which makes a very linear triode. The power trafo appears to be reasonably substantial. Visit a nearby Walmart and buy a large, plain Aluminum, cake pan. The pan will be your new chassis. Between a hand held drill and a nibbling tool, you will be able to make the drop thru opening the power trafo mounts in.I suggest you follow the example of the DECWARE SE84, for signal topology. Like the SV83 used in the SE84, the 6AQ5 is a "12" W. tube. Expect approx. 2 W. of O/P in triode mode. The 12AX7 has too much gain, once the tone controls are scrapped. Use a 12AY7 for voltage amplification duty.
You can keep the OEM O/P trafos, if you limit bass extension. An affordable upgrade is the EDCOR XSE10-8-8K.
The B+ supply in a SE amp must be WELL filtered. The simple cap. I/P filter shown is inadequate. It's easy enough to improve on what's there. Use a 5V4GA as the rectifier and save the 5Y3 for another project. You MUST take the "raw" B+ from pin 8 of the rectifier socket, when using a 5V4. Use a 15 muF. electrolytic cap. as the 1st filter element. Follow the 1st cap. with a 6 H. Triad C-14X choke, which is available from Allied Electronics. Follow the choke with a 100 muF. 'lytic. A RC decoupling section follows the CLC filter to power the 12AY7 plates.
Eli Duttman said:
Good advice on how to salvage the glass and iron, and rebuild a decent amplifier. However, I suspect most beginners would be discouraged by such a project.
Success is far more likely if he can first get the original amp working again, even if the performance is marginal. After he has a taste, there will be enough motivation to "do it right" on the second pass.
Ty,
Following that path, I suggest the following.
Replace or deactivate ALL OEM passive parts. A pair of individual L/R 100 KOhm log. taper pots. replaces the volume, balance, and tone control circuitry. Alpha brand Carbon parts from Mouser Electronics are inexpensive and quite suitable. The OEM tone controls are guano and the parts values were chosen to mate with the high impedance of a ceramic phono cartridge, not a CDP.
The issue of excessive 12AX7 gain has to be dealt with. Use a 12AY7 instead of the 'X7. 330 Ohm Carbon composition grid stopper resistors are (IMO) a good idea. Mouser carries inexpensive Xicon brand Carbon comp. resistors.
Knock out the phono I/P connector. Put a rubber grommet into the opening that's exposed. A pair of "captive" cables soldered directly to the volume control pots. will connect to the CDP.
Since this amp will never win a beauty contest, let's do something about the proximity of the power cord to an O/P trafo. Put the new, separate, L/R volume controls in the openings now occupied by the treble and loudness controls. Bring a modern 3 wire power cord in thru the opening occupied by the bass control. Put a toggle switch for turning power on/off in the opening occupied by the balance control. BTW, the labeled OEM faceplate might be removeable.
Hey, I really appreciate everyone's help. I am going to pick up some books today to learn a little more about electronics. I think I might just pick up a kit and start fresh. Maybe a k-12 or something like this
http://www.s5electronics.com/l16stereo.html
Looks that might be a good place to start, then something I can mod. I don't think I know enough to rebuild the amp with different tubes and such without a schematic.
http://www.s5electronics.com/l16stereo.html
Looks that might be a good place to start, then something I can mod. I don't think I know enough to rebuild the amp with different tubes and such without a schematic.
Dude,
You DO have a schematic.
It's the RCA original.In my previous post I suggested simplifiication. The I/Ps are connected to the "tops" of the new volume controls. The wipers of the controls are connected to the voltage amplifier grid stopper resistors. All the QUESTIONABLE circuitry from I/P to voltage gain triode is discarded.
The 12AX7 and 12AY7 are closely related. They have identical pin outs and similar electrical characteristics. The big difference between the 2 types is amplification factor (mu). The mu of the 'X7 is 100, while the mu of the 'Y7 is 40. Changes in the associated passive parts values are not essential. Just remove the 'X7 and insert the 'Y7.
Eli's right on track.
If you're going to replace all the caps and resistors anyway (possibly faster than diagnosing the bad ones) why mot simplify the rebuild and pick up all the benefits.
The fun's in getting it working, with whatever you can buy, beg, borrow. You can always improve things again tomorrow.
If you're going to replace all the caps and resistors anyway (possibly faster than diagnosing the bad ones) why mot simplify the rebuild and pick up all the benefits.
The fun's in getting it working, with whatever you can buy, beg, borrow. You can always improve things again tomorrow.
Eli, thanks. That makes much more sense. I am just getting started so I need someone to hold my hand. I just picked up a beginning electronics book so I am going to be on my way. This is the funnest part of a new hobby, picking up tidbits and letting the fog clear. I picked up a chasis fuse (no idea what value fuse to use.) For power cord I was thinking of using one from an old computer power supply with its plug. I need to get some RCA femals and some speaker posts. Once again, thanks for helping a noob!
mgalvez said:
Dude,
Think about the space available for mounting on that tiny chassis. It's very limited. I don't see where either RCA females or binding posts can go.
I suggested "captive" I/P cables previously, because of the limited space. Buy a pair of Canare F10 RCA males and several feet of Mogami W2549 "twinax" shielded cable from Markertek. You will use the Mogami shielded cable in both interconnect and chassis wire service.
An old computer power cord most definitely can be pressed into service. Cut the IEC female connector off. Crimp and solder a ring terminal onto the end of the safety ground wire.
BTW, don't forget rubber grommets where "captive" cabling passes thru chassis holes. Also, be sure to tie strain relief knots on the "captive" wiring, inside the chassis.
Before you order ANY parts, let's make sure the list for each vendor is complete. Shipping charges can eat you alive.
I built a similar tiny amp with a 6BM8/ECL82, it sounded pretty good, and with a bit of inverse feedback it actually was a nice amp to listen to, definitely more than the sum of its parts.
I concur with the other poster, the best way to improve this unit would be to totally strip all the old worn out electronic componentry and start again with a nice simple circuit, with a single volume control at the beginning. You will use the exact same tubes, transformers, but a nice simple circuit will sound better and be very easy to build. You might be able to re-use the can capacitor, but if it gets warm then it will need replacement. All other components should be new, the old ones will be shot. Tubes will be fine, it's always the passive components which don't last!
A random search turned up this circuit that should work reasonably well, and take you all of a couple of days max to build, excluding a nice wooden or aluminium chassis. From: http://www.angelfire.com/vt/audio/
I concur with the other poster, the best way to improve this unit would be to totally strip all the old worn out electronic componentry and start again with a nice simple circuit, with a single volume control at the beginning. You will use the exact same tubes, transformers, but a nice simple circuit will sound better and be very easy to build. You might be able to re-use the can capacitor, but if it gets warm then it will need replacement. All other components should be new, the old ones will be shot. Tubes will be fine, it's always the passive components which don't last!
A random search turned up this circuit that should work reasonably well, and take you all of a couple of days max to build, excluding a nice wooden or aluminium chassis. From: http://www.angelfire.com/vt/audio/
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