On the hunt for a first tube amp project/restoration.
Found this, but it's 150 miles away, and the owner doesn't have much info.
Does anyone recognize this and is it worth fixing up?
All she was able to tell me is "AMC High Fidelity"
Here's a wider view.
Found this, but it's 150 miles away, and the owner doesn't have much info.
Does anyone recognize this and is it worth fixing up?
All she was able to tell me is "AMC High Fidelity"
Here's a wider view.
That amp is remarkably similar to a console pull I have made by Magnavox. It uses a 12AX7 in which each half is used as input amp and driver for a single 6BQ5 (an excellent sounding tube) in SE class-A output. My Magnavox has slightly larger output xfmers and a large beefier 5U4 rectifier tube. I would venture to guess that you would be very suprised and pleased with what an amp like this can do on efficient speakers (~95 dB and higher). I am very impressed with mine after a simple recap and changing a few R's that had drifted off value. My amp approaches the sweet magic sound in the mids and highs of a good SETriode amp.
This amp only puts out maybe 3 watts/ch. so don't expect to rattle windows. If you are into Heavy metal this is not going to please you. If you listen to stuff like Dianna Krall this amp is a great place to start in tubes.
Distance is your problem here. Can the owner remove the amp and mail it to you so you don't have to drive 300 miles to pick up mostly firewood?
This amp only puts out maybe 3 watts/ch. so don't expect to rattle windows. If you are into Heavy metal this is not going to please you. If you listen to stuff like Dianna Krall this amp is a great place to start in tubes.
Distance is your problem here. Can the owner remove the amp and mail it to you so you don't have to drive 300 miles to pick up mostly firewood?
Thanks for the quick feedback,
I've got some high efficiency Ev's (SP12's and SP15's) which run around 100 db so high power is not the concern.
If a tube was bad - are they still around - and are they high $.
Any idea what type of ohm speaker loads these were usually built for (or was it all over the place).
I also may need to travel to the amps location for personal business anyway so getting it isn't a real problem.
/Fred
I've got some high efficiency Ev's (SP12's and SP15's) which run around 100 db so high power is not the concern.
If a tube was bad - are they still around - and are they high $.
Any idea what type of ohm speaker loads these were usually built for (or was it all over the place).
I also may need to travel to the amps location for personal business anyway so getting it isn't a real problem.
/Fred
Those tubes are easy to find and not expensive, with the possible exception of the miniature rectifier tube (EZ80?), not so EZ. If the power transformer has a 5 volt winding unused you could upgrade to an octal socket and a 5U4, 5Y3, etc.
I have a single EV SP-12 and am looking for a mate. Any chance you have an extra spare? Your SP-15's should be exceptional with this amp in the right box.
My Magnavox seems to run 4 and 8 ohm load speakers well.
I have a single EV SP-12 and am looking for a mate. Any chance you have an extra spare? Your SP-15's should be exceptional with this amp in the right box.
My Magnavox seems to run 4 and 8 ohm load speakers well.
If you will be in the area, by all means pick up the whole thing. The rest of it might save time when you discover the power connections were in the other parts. Perhaps the old speakers might give a clue as to impedance desired. etc.
RCA - I have an EV SP12B. I believe it is a recone, never used since recone. I have been keeping it for that one day when it is exactly right for something. very minor paint scratches on edge of bell and mounting holes. EV badge in center of bell intact and looks good. No photos, but could probably make some. If you might be interested in the 12B let me know.
I am in Michigan, not too far.
Decode my email from this:
first part is "tmenzo"
then the symbol for "at"
then msn
then dot com.
My line at the shop I operate is area 517, then 882-2544. I am there weekdays after 6:30PM eastern time.
RCA - I have an EV SP12B. I believe it is a recone, never used since recone. I have been keeping it for that one day when it is exactly right for something. very minor paint scratches on edge of bell and mounting holes. EV badge in center of bell intact and looks good. No photos, but could probably make some. If you might be interested in the 12B let me know.
I am in Michigan, not too far.
Decode my email from this:
first part is "tmenzo"
then the symbol for "at"
then msn
then dot com.
My line at the shop I operate is area 517, then 882-2544. I am there weekdays after 6:30PM eastern time.
Enzo said:
Enzo,
Thanx but unfortunately the SP-12B is a completely different aminal to the SP-12. The SP-12 (mine) has a much larger motor and a wizzer cone.
You didn't happen to work for a cable company and then BNR in Alberta a couple and a half decades ago did you?
Thanks again - I think I might bite on this one. Besides the travel it's only $30
Sorry - don't have a spare SP12.
I have the 15's in my "PA" speakers down in the music room (stacked on each other in this shot), the 12's are upstairs on the main stereo. Maybe this amp will end up there and some other mono amp will end up down here for guitar work.........
The ceiling in the photo is just under 7' in this room.
I've got the sound board on 1/4" spacers on the ceiling to give them alittle panel trap action as well as just overall room softening.
Sorry - don't have a spare SP12.
I have the 15's in my "PA" speakers down in the music room (stacked on each other in this shot), the 12's are upstairs on the main stereo. Maybe this amp will end up there and some other mono amp will end up down here for guitar work.........
The ceiling in the photo is just under 7' in this room.
I've got the sound board on 1/4" spacers on the ceiling to give them alittle panel trap action as well as just overall room softening.
SNAILDARTER said:
That amp is worth $30 IMO.
What kind of cabinet do you run the SP-12's in upstairs for hi-fi? Do you compliment them with a supertweeter?
BTW, seeing what you are into, if you ever run across an old Bell & Howell filmsound 16mm film projector at a Goodwill store grab it. The P-P 6V6 amp inside makes a pretty nice practise guitar amp through the 1/4" mic input jack.
The boxes for the 15's I made from some nice 13 ply void free baltic birch plywood. It came in funky 5'x5' sheets from Russia. I used WinISD (beta) for Driver specs/box and port dimensions and then compared those to the EV datasheets I had to make sure they lined up. I used Goertz copper foil inductors and Hoveland Musicaps for the cross overs.
The 12C's probably need a new home as the boxes/cross overs are not as nice and are much older than the 15A's. They're in some oak 3/4" ply. I have them set up as 3-ways with the EV horn midrange and a T35 tweeter.
The 12C's probably need a new home as the boxes/cross overs are not as nice and are much older than the 15A's. They're in some oak 3/4" ply. I have them set up as 3-ways with the EV horn midrange and a T35 tweeter.
I had no doubt the B mattered, though my 12 has a whizzer too.
I'm not your cable guy. Enzo is the name I go by though on the street. I'm strictly a Yank. Though our band played a lot in the Chatham area of Ontario back in the late 1960 and early'70s. They liked us there. US Customs sucked,though the Canadians were very nice.
I'm not your cable guy. Enzo is the name I go by though on the street. I'm strictly a Yank. Though our band played a lot in the Chatham area of Ontario back in the late 1960 and early'70s. They liked us there. US Customs sucked,though the Canadians were very nice.
Hi Snaildarter,
I would put in a vote to get the amp also. One of my first amplifier projects was messing with a Motorola stereo SE 6BQ5 amp from a mini console. Later I found a second matching amplifier in a AMC mini console. They are a different layout than the one you are looking at but quite similar in design.
One thing to look for while changing coupling caps and checking for resistors that have drifted in value is the negative feedback network. All of the little amps like these have had EQ built into the feedback network. Remove the EQ from the feedback and they sound pretty good.
Here is a crude schematic for the Motorola amps I have.
The one your looking is probably similar.
Gary P's DIY page
Good luck! Give a yell if you want to get together sometime...
Gary
I would put in a vote to get the amp also. One of my first amplifier projects was messing with a Motorola stereo SE 6BQ5 amp from a mini console. Later I found a second matching amplifier in a AMC mini console. They are a different layout than the one you are looking at but quite similar in design.
One thing to look for while changing coupling caps and checking for resistors that have drifted in value is the negative feedback network. All of the little amps like these have had EQ built into the feedback network. Remove the EQ from the feedback and they sound pretty good.
Here is a crude schematic for the Motorola amps I have.
The one your looking is probably similar.
Gary P's DIY page
Good luck! Give a yell if you want to get together sometime...
Gary
.........Well I retrieved the amp a week or so ago, fully expecting the thing to be DOA, but lo-and-behold it works. The radio tunes, and although I can see through some holes in the speaker paper they still make noise. I've de-grunged some of the wiring, gotten rid of the dust, and cleaned up the pots abit and haven't managed to kill it yet.
Attached is the schematic I've been able to trace of the amp section. The tone and volume controls are up in the radio section so those aren't covered here. I have not de-soldered anything yet so some of the capacitor values on the power supply side are as yet unknown.
What do you all think of this circuit? Should I re-cap and check resistors and leave it as is - or should I just steal the power transformer and tubes and go with a new circuit design?
Also, the output transformers just look UGLY. Looks like they've almost melted a few times in their past and I'm surprised they work at all. What specs should I be looking at for output x-fmrs for an EL84 SE design?
Thanks.
Attached is the schematic I've been able to trace of the amp section. The tone and volume controls are up in the radio section so those aren't covered here. I have not de-soldered anything yet so some of the capacitor values on the power supply side are as yet unknown.
What do you all think of this circuit? Should I re-cap and check resistors and leave it as is - or should I just steal the power transformer and tubes and go with a new circuit design?
Also, the output transformers just look UGLY. Looks like they've almost melted a few times in their past and I'm surprised they work at all. What specs should I be looking at for output x-fmrs for an EL84 SE design?
An externally hosted image should be here but it was not working when we last tested it.
Thanks.
SNAILDARTER said:
Found a bug in the schematic I drew up. Missed a ground point.
Here's the correct one.
Is 5k - 7K range for transformer about right?
rcavictim said:
Couldn't you use an EZ81.6CA4 in place of the EZ80 -- i've a few of those, and probably a couple EZ80s. They don't seem too uncommon as pulls.
I had/have 2... both slightly different, and both in sad shape (make noise but really need recones). If that is of interest i'll see if i can retrieve them.
My current amp had a similar heritage...
besides upgrading most of the parts things you can consider...
1/ replace 130R with a choke
2/ separate cathode R+C for EL84s
3/ nuke the input cap (you are unlikely to get any sources without an output cap)
4/ Triode the EL84 or try the RH84 trick (a thread on the forum goes into it)
5/ change the input tube to something with less gain
6/ and remove the feedback
The amp i have is very good... a friend has taken his even further.... (mine is actually built on his penultimate chassis with left over parts). Mine has OPTs quite similar to yours (mine are out of a magnavox)
dave
besides upgrading most of the parts things you can consider...
1/ replace 130R with a choke
2/ separate cathode R+C for EL84s
3/ nuke the input cap (you are unlikely to get any sources without an output cap)
4/ Triode the EL84 or try the RH84 trick (a thread on the forum goes into it)
5/ change the input tube to something with less gain
6/ and remove the feedback
The amp i have is very good... a friend has taken his even further.... (mine is actually built on his penultimate chassis with left over parts). Mine has OPTs quite similar to yours (mine are out of a magnavox)
dave
Attachments
First -- Thanks for all the inputs - here's an update and a question.
I've got most of the components to re-dress the amps, I'm currently waiting on some Hammond 125 OPT's. Since I plan on using this for guitar practice these should be OK for the intended purpose.
So far I've gone through and figured out how to power up the amp separately from the original console radio/phonograph hookups. There were some funny little routing in the incoming AC between the on/off switch on the radio and a tuner/phono switch so the whole console would turn off when the record finished. While doing that, and through listening to some 60Hz humm, I have upgraded to a grounded 3-prong cord so I could ground the chassis. This nicely killed the buzzing problem.
I have also experimented with taking out the feedback loop. I hooked up a switch in the path so I could toggle it in/out. WOW what a difference. Besides being louder without the feedback circuit the amp sounded more open.
To keep with the retro look - I dismanteled the original cabinet and created a new small one. I've stuffed two 8" and two 3" speakers into it. The amp will fit back inside as well, and then I can set the guitar processor on top and be set. The intent is to make something which looks like furniture so it can sit as an end table and not draw ire from the better half.
Here's the QUESTION: What is the best way to add additional inputs so I can plug in the guitar effects processor and a CD player at the same time? The effects processor can go balanced or unbalanced, currently I've been playing with it unbalanced since that is the current input config. Can I just add another RCA jack and blend them in or would the two sources not like that?
Here's a look at the cabinet with the guitar to show its size.
I've got most of the components to re-dress the amps, I'm currently waiting on some Hammond 125 OPT's. Since I plan on using this for guitar practice these should be OK for the intended purpose.
So far I've gone through and figured out how to power up the amp separately from the original console radio/phonograph hookups. There were some funny little routing in the incoming AC between the on/off switch on the radio and a tuner/phono switch so the whole console would turn off when the record finished. While doing that, and through listening to some 60Hz humm, I have upgraded to a grounded 3-prong cord so I could ground the chassis. This nicely killed the buzzing problem.
I have also experimented with taking out the feedback loop. I hooked up a switch in the path so I could toggle it in/out. WOW what a difference. Besides being louder without the feedback circuit the amp sounded more open.
To keep with the retro look - I dismanteled the original cabinet and created a new small one. I've stuffed two 8" and two 3" speakers into it. The amp will fit back inside as well, and then I can set the guitar processor on top and be set. The intent is to make something which looks like furniture so it can sit as an end table and not draw ire from the better half.
Here's the QUESTION: What is the best way to add additional inputs so I can plug in the guitar effects processor and a CD player at the same time? The effects processor can go balanced or unbalanced, currently I've been playing with it unbalanced since that is the current input config. Can I just add another RCA jack and blend them in or would the two sources not like that?
Here's a look at the cabinet with the guitar to show its size.
rcavictim said:
Hi Guys,
I'll try not to hijack this tread to far off original subject.
I just nabbed a magnavox console myself, Sounds very similar to the one described in this quote.
The Amp chassis is labeled "Amp 196-10" 1-12AX7 pushing 2 el84s
This unit is working, But, it seams to lack much bass.
So far, I havent been able to find a correct schematic. Anyone have any links that may cover this puppy?
Gene
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