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woohoo! maggie 101b on the bench

ke4mcl

ke4mcl

Super Member
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just came in via usps. maggie 101b console amp. (4) 6v6 in parallel PP mono amp. this amp seems to be a little different than the other maggies i have worked on. i see the freq crossover can like whats on the concert grande amps i have but theres no tube running in SE and theres only one OPT.

anybody got a schematic? i could use it!
 
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looks mono with only 1 opt. try yahoo/magnavox friends. they have lotta schems. in archive for dnld. dont have 101.

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How important is tube matching in paralell output sections like this? Say you had 4 tubes on each side of a push pull TX. How close do they need to match?
 
ke4mcl said:
just came in via usps. maggie 101b console amp. (4) 6v6 in parallel PP mono amp. this amp seems to be a little different than the other maggies i have worked on. i see the freq crossover can like whats on the concert grande amps i have but theres no tube running in SE and theres only one OPT.

anybody got a schematic? i could use it!
Click to expand...

Hey that looks kinda familiar.:D
I would love to see what you do with this. BTW - find a schematic, please let me know.
MArk
 
looks like i need a choke in there if i use PM speakers. may need help with that one in trying to figure out what value to use. im a noob at that.
 
From the schematic it looks like the field coil drops the voltage from 387 to 284 so right around 100v. There's also 2 coils at 250 ohms in series so 500 ohms total. 100v/500ohms= .2A or 200 ma. It looks like the tubes must be running near their limit.

You'd need a 500 ohm 200ma choke to directly replace the two field coils and maintain all the voltages on the amp. I doubt you'll find a beast like that so your best bet might be to change it to a CLCRC filter with a heavy duty high powered resistor in the R position. Maybe someone else has a better idea though.
 
Yep, I was gonna do a conversion and got side tracked. Let mine go, then decided to do one anyway. Now it's time to put the components together to do a ground up build.
HMM.......... maybe!
 
Scuzzer said:
You'd need a 500 ohm 200ma choke to directly replace the two field coils and maintain all the voltages on the amp.
Click to expand...

arent chokes usually rated in henrys? how would i find the correct value? i have quite a few chokes stripped from military gear.
 
ke4mcl said:
arent chokes usually rated in henrys? how would i find the correct value? i have quite a few chokes stripped from military gear.
Click to expand...

I don't think the henry value will be that important since you're going to end up with a large resistor as well. Something in the 1-5H range should be sufficient. Make sure it's rated for at least 400V.

Perhaps a large swinging choke input would knock off part the requisite 100v and give you better ripple rejection as well. I haven't played with that type of power supply so you might want to find one of the more educated tube guys around here to help with that. The more I think about it the better a swinging choke input sounds given the large voltage drop required.
 
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So, here's what I think I'm going to do with my 101-B. There's a good amount of space on the top deck. Fairly clean underneath, too.



If I take off the interstage transformer and the mono output transformer, I'll have gobs of room to mount a pair of Hammond 1620. I've got them leftover from a project that took a different turn. Their 6.6K load is perfect for a single pair of 6V6. All I should need to do is punch two or three holes for the driver tubes, and I'll have a nice 12 watt push/pull stereo 6V6 amp. Who's got the right schematic for me?

 
you going to use 12ax7's? I started a thread about premium 6v6 PP amps(maybe a week ago). It has a lot of schematics in it that would likely work for you.
Good luck
 
Jcricket said:
you going to use 12ax7's?
Click to expand...

I want to use something 9-pin for the drivers. I've got buckets full of 12--7 tubes: AX, AT, AU, BH, AV, and even a few AY. I only have a couple 6SL7GT, and only one 6SN7GT so going all octal would be a little more awkward.

The Hammonds have UL taps, so I'd like to use them if I could. I don't know how well the 6V6 works in ultralinear. It seems that some of the more highly regarded designs advocate using the 6V6 in triode-strapped configuration. For now, my favorite designs include the following:

Dynaco "Low Power" Amp
Ultralinear finals,
Front end: ???
http://www.triodeel.com/dyna6bq5.gif

Dynaco Stereo 35
Ultralinear finals,
Front end: 12AX7 gain stage DC coupled to 12AU7 cathodyne
http://www.triodeel.com/dynast35.gif

see also Sy's Red Light District for similar topology,
but with 12AT7 and pentode finals
(http://syclotron.com/rld_signal_circuit.jpg)

El Cheapo
Triode strapped finals,
Front end: 12AT7 long tailed pair w/ CCS
http://homepage.mac.com/planet10/forum/elCheapo-23jun06-map.gif

Musical Machine
Triode strapped finals,
Front end: 12AV7 long tailed pair w/ negative supply
http://www.audiotropic.net/Projects/implement.html

I'm probably leaning towards the Dynaco "Low Power" right now. It uses the ultralinear taps, and doesn't require the construction of any CCS circuits or negative supply rails. I suppose my second choice would be El Cheapo. I've already got a couple EL84 based ST35 clones around, so I'm not in a hurry to make another one.
 
As someone above suggested, I think the field coil speakers played some part in keeping the voltages in line. Line voltage was probably 10% lower in 1950, which doesn't help either. It might be time to rethink the power supply a little. It seems that big honking power transformer isn't just there for show. No load, I'm seeing about 405-0-405 off the HT winding. That's not going to work for a cap input filter if I plan to run 6V6. My B+ will be way past the sensible working voltages for the tubes. Might have to think about a choke input supply?

The DCR of the HT winding is about 75 ohms. That implies this PT is good for about 190 mA cap input, or about 260 mA if I go choke input. Choke loaded, the supply should work out to around 335 VDC with a 5AR4 rectifier. That might work... just need a good choke.
 
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