Hello All;
This is my first post here, I have been hanging out guitar tube amp forums for quite a number of years and have lots of guitar amp builds under my belt. Have wanted to get into the audio end for some time but with my new builds and guitar amp repair it has kind of kept me away.
What got me here today is that my shop amp re: old Pioneer solid state, went tits up on me. So I'm thinking this is my chance. I got a 450 sqft shop, some little JBL bookcase speakers, I want an amp that I can run my sat receiver, CD player and computer through. Since these signals are relatively small do I need a preamp and a power amp?
What do I need....I don't know. How many watts.....I don't know. But when I dime my tweed 5 watt Princeton in the house all I see is my wifes mouth moving and steam coming out her ears. I get the point and move to the shop.
I have quite a bit of components and hardware for guitar amps. I like to build from scratch, including drilling and setting turrets. Really I'm just kind of at a loose on where to start.
Any suggestions?
Hers a couple of my amps.
BL
This is my first post here, I have been hanging out guitar tube amp forums for quite a number of years and have lots of guitar amp builds under my belt. Have wanted to get into the audio end for some time but with my new builds and guitar amp repair it has kind of kept me away.
What got me here today is that my shop amp re: old Pioneer solid state, went tits up on me. So I'm thinking this is my chance. I got a 450 sqft shop, some little JBL bookcase speakers, I want an amp that I can run my sat receiver, CD player and computer through. Since these signals are relatively small do I need a preamp and a power amp?
What do I need....I don't know. How many watts.....I don't know. But when I dime my tweed 5 watt Princeton in the house all I see is my wifes mouth moving and steam coming out her ears. I get the point and move to the shop.
I have quite a bit of components and hardware for guitar amps. I like to build from scratch, including drilling and setting turrets. Really I'm just kind of at a loose on where to start.
Any suggestions?
Hers a couple of my amps.
BL
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Wellcome aboard!
There are plenty of amp designs around on the forum. One of the favorites lately has been Pete Milletts "engineers amp":
http://www.diyaudio.com/forums/tubes-valves/151206-posted-new-p-p-power-amp-design.html
Which does anywhere from 18 Watts to 250 Watts per channel with some mods using Sweep tubes. I'm sure others here will drop in with some other popular amp suggestions as well. Then there are many "classic" designs that get built too. Dynaco amps for example. Mullard 5-20. ....
There are plenty of amp designs around on the forum. One of the favorites lately has been Pete Milletts "engineers amp":
http://www.diyaudio.com/forums/tubes-valves/151206-posted-new-p-p-power-amp-design.html
Which does anywhere from 18 Watts to 250 Watts per channel with some mods using Sweep tubes. I'm sure others here will drop in with some other popular amp suggestions as well. Then there are many "classic" designs that get built too. Dynaco amps for example. Mullard 5-20. ....
BL,
The amount of power you need depends of the efficiency of the speakers. Do you have the spec's for the speakers? By any chance, do you know what the JBLs' crossover is like? What was the power rating of the dead SS unit?
Unless you get involved with phono, you will not need a preamp with gain. You have described "line level" sources and a stereoblock "integrated" amp will be fine.
The amount of power you need depends of the efficiency of the speakers. Do you have the spec's for the speakers? By any chance, do you know what the JBLs' crossover is like? What was the power rating of the dead SS unit?
Unless you get involved with phono, you will not need a preamp with gain. You have described "line level" sources and a stereoblock "integrated" amp will be fine.
Speaker I have been using are JBL 2600s and the dead tuner/amp is a Pioneer SX-V200. I'm tring to get a handle on the differences between SE and PP, I know the differences as far as how the crcts work. More about how they sound in an audio application. I've got some iron from an old Bogen integrated P-P amp running 7408/6V6s. But you know parts are not really a problem. And although I don't have anything against crct boards I really like the hand wired/turret boards. But then again I'm open.
Maybe some suggested reading?
BL
TW Rocket Gut Shot I built from scratch. I didn't punch the chassis.
Maybe some suggested reading?
BL
TW Rocket Gut Shot I built from scratch. I didn't punch the chassis.
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BINGO! Build an "El Cheapo" with those O/P trafos. While 6 WPC from triode wired 6V6 family tubes is not a lot of power, the project is a cheapskate's delight and sounds very good. If by chance Bogen used UL taps, you can tie the g2 resistors to those, instead of the plates, and get 12 pretty darned good WPC. A full set of power "iron" can be ordered from Allied Electronics, at modest expense, should you be interested.
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I got the PT out of Bogen also. No UL taps. I've also got some got an Edcor EM0725A 650V/400mA PT, an EM0726 600V/250mA PT,EM0731 640V/250mA. What I don't have is a lot of is audio OPTs. Just the Bogans, but I dont mind buying more iron.
If you wouldn't mind the attachment doesn't blow up to well, would you e-mail me a copy. 1blindlemon at cox dot net
BL
If you wouldn't mind the attachment doesn't blow up to well, would you e-mail me a copy. 1blindlemon at cox dot net
BL
Morgan Jones: Valve Amplifiers.
Love your chassis wiring and construction technique. Might be worth tweaking a thing or two for your next build, but really nice effort nevertheless.
- Frank.
EL Cheapo
I can highly recommend this project, particularly if you have a scrap box of parts.
In my case the major organ donors for a pair of these were old Scott LK48 /222 amps, which required some revisions to Eli's circuit to take advantage of existing parts etc., so I ended up using EL84s, connected in triode due to the lack of UL taps, as well as a PCB kit from Greg at Classic Valve for the LTP CCS.
Unfortunately the complete tube set for this amp put a lot of thermal load on the power transformer for filament supplies (IIRC something like 9 novals plus the rectifier, and one went Chernobyl a couple of years back.
I finally got around to recycling the very fine OPT into another project with Pentode operation. As sweet as the triode sounds with 92+dB sensitivity Fostex full-rangers, the extra grunt of pentode is hard to ignore on speakers like the Mark Audio/CSS EL70 / Alpair 7 that I've been playing with lately.
I can highly recommend this project, particularly if you have a scrap box of parts.
In my case the major organ donors for a pair of these were old Scott LK48 /222 amps, which required some revisions to Eli's circuit to take advantage of existing parts etc., so I ended up using EL84s, connected in triode due to the lack of UL taps, as well as a PCB kit from Greg at Classic Valve for the LTP CCS.
Unfortunately the complete tube set for this amp put a lot of thermal load on the power transformer for filament supplies (IIRC something like 9 novals plus the rectifier, and one went Chernobyl a couple of years back.
I finally got around to recycling the very fine OPT into another project with Pentode operation. As sweet as the triode sounds with 92+dB sensitivity Fostex full-rangers, the extra grunt of pentode is hard to ignore on speakers like the Mark Audio/CSS EL70 / Alpair 7 that I've been playing with lately.
Ok.....got a closer look at the schematic and I'm not sure I understand everything I see with the constant current LPT. The Bogan PT mains aren't CT'ed so I'd have to use a FWR although it does filament and another couple of yellow wires that if this thing had a CT I'd guess they were Rect filament wires. May need some help converting this to the iron I have.
BL
BL
I did some digging at jbl.com and came up with some spec's, for the 2600s. Nominal impedance is 8 Ω and sensitivity is a 89 dB. SPL at 1 M. driven by 1 W.
Given the 450 ft.2 shop, I'm going to suggest an ultralinear mode 7591 based "El Cheapo Grande". That will yield 30+ honest W. and allow some cranking to be done.
Other than allowing for the requisite "taller" B+ rail, the 12AT7 based splitter/driver requires no changes. Edcore's $62.27 model CXPP60-8-6.6K O/P trafo will work well, without causing bankruptcy.
Given the 450 ft.2 shop, I'm going to suggest an ultralinear mode 7591 based "El Cheapo Grande". That will yield 30+ honest W. and allow some cranking to be done.
Other than allowing for the requisite "taller" B+ rail, the 12AT7 based splitter/driver requires no changes. Edcore's $62.27 model CXPP60-8-6.6K O/P trafo will work well, without causing bankruptcy.
Ok, If I read it right the tubes will pull ~80/104ma ea plus a little more on top of that for the 12AX7. Will my EM0731 640V/250mA running a GZ34 be a big enough PT and provide the requisite plate voltage or run FREDs. I'm thinking the Edcor EM0725A 650V/400mA PT I have would be over kill? Plus since this amp is cathode biased I wouldn't need the 50V bias winding. Or am I not understanding the PT and rail requirements.
I know I'm not understanding the phase inverter compared to a guitar amp PI.
BL
I know I'm not understanding the phase inverter compared to a guitar amp PI.
BL
IMO, a combination bias scheme is best, in an "El Cheapo Grande". Current production 7591s will not tolerate a violation of the grid to ground resistance limit. OTOH, if the grid to ground resistance is low, LTP gain will fall below that needed to drive the "finals" and the NFB loop. "Standing" each pair of 7591s on a 100 Ω/47 μF. bias network protects against run away, doesn't drop that many Volts, and provides a very convenient test point for setting the "idle" current. The bulk of the bias voltage comes from a C- supply. Use 270 KOhm grid to ground resistors with confidence. Even 330 KOhms is probably safe.
The constant current sink (CCS) in the LTP's tail forces symmetry between the 2 sides. When the current on 1 side increases, the current on the other side must decrease. The coupling at the cathodes is "perfect" and allows the I/P signal applied to the inverting triode's grid and the NFB signal applied to the non-inverting triode's grid to interact correctly.
BTW, the LTP is a 12AT7, not a 12AX7. High gm and low RP are your "friends" in driver circuitry. The 'X7 totally lacks those characteristics.
Even 330 KOhms is probably safe.The constant current sink (CCS) in the LTP's tail forces symmetry between the 2 sides. When the current on 1 side increases, the current on the other side must decrease. The coupling at the cathodes is "perfect" and allows the I/P signal applied to the inverting triode's grid and the NFB signal applied to the non-inverting triode's grid to interact correctly.
BTW, the LTP is a 12AT7, not a 12AX7. High gm and low RP are your "friends" in driver circuitry. The 'X7 totally lacks those characteristics.
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