Maggie Console Rebuild: Chapter 1: The Premise

[Harlon]

To Change Bias or not to Change Bias

I've started a side thread specifically asking about Dave's EFB circuit.
I've seen it suggested, including in this thread, that it be used in association with UL power output.
I'm looking for anyone who has applied the circuit to one of these hybridized amps.
Lots of people say it's great, and from what I've read it looks great.
Likewise looking to find out if it is compatible with my application. If I go with the dynaclone opts it makes sense. I likely will go with the Edcors. Would it work equally well with them?

 

[dcgillespie]

EFB can be applied to any push-pull output stage (triode/UL/pentode) that operates in some form of Class AB. It can be applied to a purely Class A amplifier as well, but since current flow in such an output stage is nearly constant at all output levels, it serves little purpose as the near constant current draw causes there to be little shifting of the operating point.

Dave

 

[s-petersen]

Sorry for the ignorance but what does that mean in Internet speak?

It means that I don't have anything to add, but I'm watching the thread,(lurking in the shadows) I usually jump in when the conversation slows down, and I have some info to add. I am at work(nights)so I am not able to watch too much at the moment

 

[s-petersen]

When you replace the output transformers, you should use a known circuit (like the Dynaco circuit with the z565 transformers), unless you have a signal generator and scope. For best results the feedback loop needs to be tuned to the transformers used.

 

[Harlon]

When you replace the output transformers, you should use a known circuit (like the Dynaco circuit with the z565 transformers), unless you have a signal generator and scope. For best results the feedback loop needs to be tuned to the transformers used.

Yeah, I'm concerned about being able to get it right with the Edcors because all I have is a mm. If this becomes a life long thing I'll likely end up with a generator and scope in my shop, but not today.

 

[Harlon]

H,

Can you still see the two numbers stamped on your PS tranny? Is one 300195-1?

Yes, the other is 1886228.
Why?

 

[Harlon]

There is a kind of discrepancy or something with the parts list description of that tranny. I have a 9304 chassis and a 9302 chassis both have that. But the parts list of the 9302 chassis describes it has having a 130ma secondary rating. It doesn't take the tuner or MPX unit draw into consideration. But on another diagram I have without a parts list it says consoles with the tuner and MPX have beefier trannies. So do you have a specific 9304-20 manual with a parts list showing the 300195-1 as being heavier than just 130ma on the high voltage secondary?

I'm stepping out but I'll check later.

 

[Harlon]

I'm stepping out but I'll check later.

Plans changed.
The sheet I have has the 130mA. As all of these units had some level of satellite equipment that they were running perhaps this was the convention. Both the MPX and tuner schematics I have show 40mA riding with the B+ coming into he unit through the molex.

Perhaps one of the experts here at AK can shed some light.

 

[Harlon]

Well that's interesting. On your diagram of the PS circuit, is there a 250v source line? None of my schems has a 250v line. I just wonder if the one you posted of the Molex connector showing the 40ma load and 250v source was getting it from a different part of the PS and a different rectifier on the tuner.

You can see in the shot of the tuner power section that there isn't a rectifier there. Whenever I get to work on modding the ps I'm going to do some continuity testing so I can break things down and figure out where everything is going. With it running through the MPX to the tuner and back it's just beyond me.

 

[jazbo8]

My intent is to rebuild and refurb all parts of the console so that I can benefit from the best of the improvements available to the 9300 series amps while still using the stock tuner, MPX and TT.

The biggest improvement is likely going to be replacing the speakers, epecially if you can only play the console at modest/low volume. None of the improvements that you are considering including the EFB and other circuit modifications will shine unless you can "pump up the volume" as they say...

 

[Harlon]

Does your diagram of the PS outputs show a 250v source line? Mine shows 325v. going to the tuner. I don't have the tuner schems.

You may reach out to Tom Bavis here on AK. He helped me with a couple of schematics early on. Unfortunately my unit doesn't match the sams precisely apparently kind of like all the 93xx varieties, they would come out with variants and the old techs knew enough to work around it.
I just started a thread asking for identification help with some photos and help materialized pretty quickly.

 

[Harlon]

Power Supply Update

For the power supply I am going to go with the basically stock 5u4GB based ps in Battradio's 93xx modded schematic. 47uf/5h/100uf/100uf. If I find later on that I need a little more power I will convert to SS, but right now sticking with the Maggie source with a little more inductance and capacitance seems like the way to go.

I'm going to be doing the amp portion of my rebuild in a 4 phase fashion.

Phase 1.) Full rebuild with better quality(thinking auricap xo) caps and changing all resistors. Installing a new matched quad of EL84Ms from Mcshanes.

Phase 2.) Install EFB in the upgraded yet stockish configuration.

Phase 3.) Install Edcors, or Z565s if I can swing it.

Phase 4.) Go UL with the new opts.

Kind of step by step to see how each upgrade improves the sound quality.

During downtime between amp iterations I will be doing the refurb on the rest of the console.
Sometime this weekend I'm going to put in orders for the Edcors, new tubes and all the parts I'll need for phase 1 and recapping the filtering sections of the MPX and tuner. Fairly certain I'm going to send the TT out for refurb.

I really really want to go with one of the dynaclones for the opts, but every time I look at the price I cringe a little.

 

[Harlon]

The biggest improvement is likely going to be replacing the speakers, epecially if you can only play the console at modest/low volume. None of the improvements that you are considering including the EFB and other circuit modifications will shine unless you can "pump up the volume" as they say...

They'll be near the end of this adventure, but speakers will eventually be part of the new formula.

 

[Harlon]

Just thouht we might be able to quickly figure out how a 130ma tranny could supply 130ma + 40ma. But if that shot of the Molex and your schems aren't representative of the amp then it's going nowhere. That power could be from a diode on one of the other units with A/C for the TT motor.

There's nothing in the schematic that I can see.
When I sit down to recap the ps on the amp I'll be replacing the filters throughout the unit. I'll do continuity testing to find out what's going where and amperage readings on everything so I can find out what's not on the schematics.

 

[Harlon]

Silver Mica Cap Replacement Values

Quickie:

Ordering parts for the refurb. C105 and C205 are 100 mmf caps. I'm replacing these with 100 pf caps. Is a voltage rating of 500 sufficient for these caps?

 

[Harlon]

The originals are 400v.

Thanks

 

[gadget73]

Yes, but those are probably fine. The small value caps are ceramic and last a very long time. They are mostly used to stabilize it at high frequencies.

 

[Harlon]

Yes, but those are probably fine. The small value caps are ceramic and last a very long time. They are mostly used to stabilize it at high frequencies.

Yeah, I'm on the fence about swapping them but everything else is changing so I don't want them to be jealous. And they only cost a 30 cents so,...

 

[Harlon]

First Parts Order Hurrah

Just placed the first order for this project.

I decided at some point to start at the power supply for the amp and console. Figured that if I build a solid smooth power base that I would be able to get the most out of the modifications that will be forthcoming.

BattRadio(Mark), and Levane helped significantly in the development of my new power supply. I think Mark got tired of all my questions and decided to teach me how to fish. Hooked me up with a link to PSUD2 which I recommend to anyone with a desktop. I'm no expert, but it helps you see the impact of upping capacitance, or dropping in an extra choke or what not on the voltage ripple.

I'm going with the stock transformer and 5U4GB rectifier. Dropping to a 33uf reservoir cap so I can play with swapping in a 5AR4 down the road. This followed by three 1.5 henry chokes linked with two 47uf smoothing caps. Finishing up with a pair crc 470uf caps.

If you have any technical questions, put it in PSUD2 and see what it does to the voltage ripple.

My initial plans were to go 40/5henry/100/100. Mark suggested the multiple chokes and suggested I take a look on PSUD2. Ended up with better voltage ripple and less $$$ for a pair of 1.5 henry chokes(I already had one) than one 5 henry. Won't look quite as cool on the deck, but that's not everything.

Per another thread I started inquiring about a universal ps for 9300 and 175/185 and 8802 amps, I am going to build my ps on a separate chassis. It's also a space issue on the 9304-20 with 2 extra chokes and 2 monster caps. For now I'm going to utilize a philco amp chassis I have laying around. I'm going to strip the philco while I wait for the parts to arrive.

Soon I'll throw up some before pics of the mess of an amp I'm starting with.

Thanks to everybody on AK who helped me get to this point.

 

[Lavane]

Have you got a drawing of the new PS? I would like to see it. My wife uses a 175 I did but doesn't really want me to in her words "mess with it too much". I would like to put a better PS in it but the rectifier tube has to stay. She doesn't think the SS one I used on the 9303 looks good.