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RH84'ing the 8601....

C

chingon

Well-Known Member
So I've decided to rework my maggie but convert into an rh84 circuit. It will be a full strip but will reuse the iron and tubes (driver not w/standing). I want to implement the choke(s) necessary for this thing to be dead silent. What I need now is guidance from the ak community as to how to carry through with this thing.

1st and foremost....the transformers are not what the rh84 circuit calls for. How does this affect the values and topology of the components (can i stick w/original values)?

Same question as above if using maggie rectifier 6ca4 as opposed to rh's 5u4. If price difference isn't much would sticking to the 5u4 simplify things?

I've had a hard time finding a new choke that fits the parameters the Rh circuit calls for (20H min, 50 mA) at a low price. I've read that using a pair of radiodaze chokes (RDC-100 8H, 125 mA @ http://www.radiodaze.com/RD-transformer01.htm) are an ideal solution. How does this affect the layout of the rh84 circuit and its values?

And lastly, what type of capacitors (PIO, electrolytics, etc..) and resistors (carbon, ceramic, wattage) are recommended for each of those components pictured in the rh84 schematic?

I know I'm asking a lot here, basically almost a redrawn circuit to make my stuff work, so I appreciate the fact that you are still reading at this point. I know a few out there would like to follow a similar path.

In not so many words:
Rh84 with the following caveats:
8601 power and output transformers
6ca4 rectifier (not set in stone)
ecc81 12at7 driver
pair of radiodaze chokes

I've attached the rh84 and maggie circuits for reference

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You can redesign the power supply to your heart's content--I used a 6CA4 in my build and I plan to use it on my next build--but just so long at your B+ is when the rest of the circuit calls for, then you should be fine. :thmbsp:

Do a search for Duncan's PSU Designer.

Also verify that you've got 5k as your primary impedance with the OPTs you've got on hand.


:lurk:
 
For stereo the current doubles - caps would be double and choke half the value for same ripple reduction. However, the input capacitor shouldn't exceed 40 uF for either rectifier (possibly a little more, depending on the transformer winding resistance). Bypassing the screen could help reduce hum somewhat if that's a problem. 6CA4 is superior in my mind, due to slower warmup and lower voltage drop - its 150 mA rating is more than enough. Move it to the other 6.3V winding so there's no worry about coupling noise via heater winding. Anyway, there's no 5V winding - and the free 6.3V winding may not have 3A capacity for a 5U4.
 
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chingon said:
So I've decided to rework my maggie but convert into an rh84 circuit. It will be a full strip but will reuse the iron and tubes (driver not w/standing). I want to implement the choke(s) necessary for this thing to be dead silent. What I need now is guidance from the ak community as to how to carry through with this thing.

1st and foremost....the transformers are not what the rh84 circuit calls for. How does this affect the values and topology of the components (can i stick w/original values)?

Same question as above if using maggie rectifier 6ca4 as opposed to rh's 5u4. If price difference isn't much would sticking to the 5u4 simplify things?

I've had a hard time finding a new choke that fits the parameters the Rh circuit calls for (20H min, 50 mA) at a low price. I've read that using a pair of radiodaze chokes (RDC-100 8H, 125 mA @ http://www.radiodaze.com/RD-transformer01.htm) are an ideal solution. How does this affect the layout of the rh84 circuit and its values?

And lastly, what type of capacitors (PIO, electrolytics, etc..) and resistors (carbon, ceramic, wattage) are recommended for each of those components pictured in the rh84 schematic?

I know I'm asking a lot here, basically almost a redrawn circuit to make my stuff work, so I appreciate the fact that you are still reading at this point. I know a few out there would like to follow a similar path.

In not so many words:
Rh84 with the following caveats:
8601 power and output transformers
6ca4 rectifier (not set in stone)
ecc81 12at7 driver
pair of radiodaze chokes

I've attached the rh84 and maggie circuits for reference
Click to expand...

Basically if I was to do it again I would not bother with a choke - just use a "relative voltage regulator" consisting of a high voltage mosfet like the IRF 730, IRF 740, IRF 830, IRF 840 etc., a zener , one capacitor and a couple of resistors. Mount them somewhere out of sight and where it does get a bit of cooling. (Mostfet need mounting on the chassis so it does not overheat)

(Please see my recent postings on my 6L6GC "RH807" clone.)

Recommend 2 watt resistors from AES for all high voltage stuff, the (modern) smaller 0.4 / 0.5 / 0.6 W resistors just are not build to go up to the high voltage levels used (you may get away with it but for all the work I would not risk it).

Some like the sound of the 12AT7, I prefer the sound of the 12AX7 and have changed the resistor values accordingly.

All the RHxx amps have a similar "sonic signature" and "rolling (output) tubes" makes only minimal difference.

Good luck.

AM
 
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I'd hang onto the 6CA4, if for no other reason than you've already got it and the correct socket for it. The power supply for the RH84 is a conventional capacitor input setup with a choke instead of a resistor for the first drop. You can easily sub the 6CA4 for the 5U4.

The 6EU7 is basically a low noise 12AX7 with a different basing, so if you modify your resistor values to take a 12AX7 tube, you can retain the 6EU7.Just keep in mind the pins are in different spots.
 
thefragger said:
You can redesign the power supply to your heart's content--I used a 6CA4 in my build and I plan to use it on my next build--but just so long at your B+ is when the rest of the circuit calls for, then you should be fine. :thmbsp:

Do a search for Duncan's PSU Designer.

Also verify that you've got 5k as your primary impedance with the OPTs you've got on hand.


:lurk:
Click to expand...

This is what i've got from the sams. I downloaded the software but there are some values I don't know, not to mention I'm an ME and my knowledge of circuits is very limited (I can read them to a certain point but can't design them).
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Tom Bavis said:
For stereo the current doubles - caps would be double and choke half the value for same ripple reduction. However, the input capacitor shouldn't exceed 40 uF for either rectifier (possibly a little more, depending on the transformer winding resistance). Bypassing the screen could help reduce hum somewhat if that's a problem. 6CA4 is superior in my mind, due to slower warmup and lower voltage drop - its 150 mA rating is more than enough. Move it to the other 6.3V winding so there's no worry about coupling noise via heater winding. Anyway, there's no 5V winding - and the free 6.3V winding may not have 3A capacity for a 5U4.
Click to expand...

hmm..i thought the circuit (rh84 pictured) was while showing only one channel, with the correct values for components used in stereo.

it seems the 6ca4 filament can be powered by the lower current 6.3 v tap without problem. The spec sheet lists max capacitance at 50 uF, should I still stick w/40?
 
chingon said:
So I've decided to rework my maggie but convert into an rh84 circuit. It will be a full strip but will reuse the iron and tubes (driver not w/standing). I want to implement the choke(s) necessary for this thing to be dead silent. What I need now is guidance from the ak community as to how to carry through with this thing.

1st and foremost....the transformers are not what the rh84 circuit calls for. How does this affect the values and topology of the components (can i stick w/original values)?

Same question as above if using maggie rectifier 6ca4 as opposed to rh's 5u4. If price difference isn't much would sticking to the 5u4 simplify things?

I've had a hard time finding a new choke that fits the parameters the Rh circuit calls for (20H min, 50 mA) at a low price. I've read that using a pair of radiodaze chokes (RDC-100 8H, 125 mA @ http://www.radiodaze.com/RD-transformer01.htm) are an ideal solution. How does this affect the layout of the rh84 circuit and its values?

And lastly, what type of capacitors (PIO, electrolytics, etc..) and resistors (carbon, ceramic, wattage) are recommended for each of those components pictured in the rh84 schematic?

I know I'm asking a lot here, basically almost a redrawn circuit to make my stuff work, so I appreciate the fact that you are still reading at this point. I know a few out there would like to follow a similar path.

In not so many words:
Rh84 with the following caveats:
8601 power and output transformers
6ca4 rectifier (not set in stone)
ecc81 12at7 driver
pair of radiodaze chokes

I've attached the rh84 and maggie circuits for reference

attachment.php


attachment.php
Click to expand...



Chingon,

You can re-use the OTs from your Maggi if they have 5K impedance, like I did use mine from original old RCA console amp. The sound is very good even I use it with the cheap Chinese preamp. "Guanzo". Photos below.

For power supply I used the original power transformer, doubler, with SS rectifier. I did the same as Fragger suggest early, I used Duncan's PSU Designer to design the power supply, and mine it deadly quiet. If you use tube for recitfier then choke will help to reduce noise.

I used The Russia PIO caps for signal and the rest for whatever I have in hand.

Good luck on your rebuild, you will never reget to go for it :thmbsp:
 

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50 uF should be fine - this is a small transformer, so winding resistance will limit peak rectifier current - which is the REAL limit. You'll need about 90 mA for two channels. If you're using the existing chassis, you will have to choose a choke that FITS, and select other power supply components to give the necessary ripple reduction. Since there won't be much AC voltage across the choke, mounting position won't be critical.
 
If it were me, I'd leave the 6CA4 rectifier in place. It'll do fine.

I'd make the first cap in the power supply 47uF@450V. It'll be a more common part, it'll be cheaper, it'll be very voltage tolerant, and it'll be about as large as you'd want to make it without making it too large for the rectifier. You want your final VDC to be closer to 300VDC, going from a 40uF cap to a 47uF cap will help increase your overall voltage very slightly.

I'd put the radiodaze RDC-100 choke next, after the 47uF cap. Then I'd put a large cap next, like 220uF @ 400 VDC. You might be able to just do that and call it a day for B+.

After that, each channel would get it's own RC stage for the 12AT7 driver tube.
 
If I had two RDC-100 chokes, and another cap, I'd put another LC stage after the first one.

First supply to try:

C1 -> L1 -> C2

C1: 47uF@450VDC
C2: 220uF@400VDC
L1: RDC-100 choke

Improved:

C1 -> L1 -> C2 -> L2 -> C3

C3: 220uF @400VDC
L2: RDC-100

After those filter chains, you'd follow the schematic for the RH84 and give each 12AT7 section it's own RC stage (10K -> 10uF@350V, as per the schematic).
 
I built an 8601 into an RH84 and it does sound superior to the maggie circuit. However, make sure you re-do the cathode resistors to adjust for lower B+...the highest the magnavox can do with the 6CA4 and a 47mf cap is around 280v. Mine has problems with hum because there is NO room for a choke...this one would be a good candidate for cpacitance multiplier (gyrator) or mosfet regulator. I have not actually tried this yet, however I disconnected the B+ and hooked up my Eico power supply and the circuit was dead quiet again.
 
thanks a lot for the input guys, i'm loving it. I may try to relocate some things around and put the chokes on the chassis or mount them off board but I'll try to still put them on there.

I'm mucking w/duncan's software but i've hit a snag. Basically w/values relating to impedance and resistances on the components and load being seen. Been years since I've done anything ohm's or kirchoff's related (and wasn't the greatest student in the class to be honest). Take squidward's suggestion for the 1st psu for example:

I changed the transformer's secondary to 460 volts, but don't know what impedance to put in there (can I do this w/o busting out the multimeter and measuring resistance at the tap)? I'm guessing it's not as simple as solving for R in V=IR since this is impedance right?

same w/capacitors and choke's resistance. The load I put as the value for one of the output transformers....which i'm sure is wrong both in value and knowing there are two outputs..

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Squidward said:
Improved:

C1 -> L1 -> C2 -> L2 -> C3

C3: 220uF @400VDC
L2: RDC-100

After those filter chains, you'd follow the schematic for the RH84 and give each 12AT7 section it's own RC stage (10K -> 10uF@350V, as per the schematic).
Click to expand...


am i doin it rite ??
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Thespeakerdude8 said:
. Mine has problems with hum because there is NO room for a choke...this one would be a good candidate for cpacitance multiplier (gyrator) or mosfet regulator.
Click to expand...

Amadeus Mozart hinted to this above....don't think I forgot about you Wolfgang....

To mr Mozart, was the choke not to your liking or why would you do it again w/your recommended solution?
 
None of these amps will win a beauty contest. Put the choke on top, if that's the only place you can squeeze it in. If you only have room for 1 choke, give the simpler PS a shot.

thespeakerdude says with a 47uF cap input, you'll hit around 280VDC for B+. It's not bad, maybe a little low. You could change the value of the cathode resistor, like he says, to compensate if you're worried about full power.

I don't use the sim software, so I can't help you there!
 
Squidward said:
None of these amps will win a beauty contest. Put the choke on top, if that's the only place you can squeeze it in. If you only have room for 1 choke, give the simpler PS a shot.

thespeakerdude says with a 47uF cap input, you'll hit around 280VDC for B+. It's not bad, maybe a little low. You could change the value of the cathode resistor, like he says, to compensate if you're worried about full power.

I don't use the sim software, so I can't help you there!
Click to expand...

Thanks for the answers....I just came across the hammond 193c choke. It's closer to spec 20 H, but 100 mA. It would come to around 45ish shipped as opposed to the 25-30 radiodaze pair, but mounting seems doable. I don't know how inductance plays in this particular circuit, so what compromises am I looking w/a lower H value as opposed to a higher? There's also a hammond 157g 30 H, 40 mA (10 mA lower than what circuit calls for) that perhaps is suitable?

Do you think your choke pair would prove superior (maybe cheaper) than going w/the hammond?

thanks for the patience...

PS: OK, I went with the hammond, they only had one in stock and I had to act quick. I'd still love to hear what your take is on those questions though
 
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I would go as Squids first power supply suggestion, an only 1 choke circuit, you'll
loose to much voltage trying to get 2 choke circuits in there not to mention room.
(use whatever choke you want, the supply topology would be the same)

Here is how the PSUDII would be setup, your voltage is half what the power tranny
voltage listed, as that is across the 2 outside windings, not center tap to either leg,
also with today's wall voltage it is slightly higher, 40ohms is a guess an close enough
to get a understanding of the supply, I use 1 ohm for caps, current is the whole amp
and this should be pretty close including both outputs an drivers.

Have fun!
 

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Kegger said:
I would go as Squids first power supply suggestion, an only 1 choke circuit, you'll
loose to much voltage trying to get 2 choke circuits in there not to mention room.
(use whatever choke you want, the supply topology would be the same)

Here is how the PSUDII would be setup, your voltage is half what the power tranny
voltage listed, as that is across the 2 outside windings, not center tap to either leg,
also with today's wall voltage it is slightly higher, 40ohms is a guess an close enough
to get a understanding of the supply, I use 1 ohm for caps, current is the whole amp
and this should be pretty close including both outputs an drivers.

Have fun!
Click to expand...

Ok, i followed your example and this is what I came up with:


The single radiodaze PSU has the least voltage drop

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The dual has more voltage drop
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The hammond 193c has higher voltage drop than the single radiodaze, but less so than the dual.
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The hammond 157g has the highest voltage drop (guessing çuz of 454 ohm resistance).
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So from a voltage drop point of view, it seems I made a mistake ordering the hammond choke as opposed to the radiodaze, but I can't help but think there's more to it? why was the 20 h recommended as opposed to a lower one in the rh circuit? Should I cancel my hammond order and go w/the radiodaze?
 

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