Motorola console tube amp conversion help with pics

JMicro

New Member
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I am rebuilding/ converting a Motorola console amp HS-621 year 1957( golden voice) all the resistors and caps where cut out before I got it. I have the Sams and Beitmans. I am looking for anyone that drew up a wiring layout or has good photos of one thats been restored underneath. Im trying to stick close to the original but its hard to understand all of the actual wiring layout from the schematic the Sams (from Sams website) doesn't have the greatest scan of the underside.Also some large caps from the original Sams cover some sockets.
Thanks for any help.

I cleaned it up/ de-soldered cut out parts and started the build here is what I have so far. Pretty clean unit. Has nice iron on it. I replaced the 2 12au7 sockets with new ones of better quality. Added fuse, indicator light, switch and IEC socket (fun) . Also I removed the second RCA jack input I am going to use the input next to volume pot. Also I plan to use all metal oxide resistors.

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HS-621.jpeg Here is the schematic I am using says it for HS-606 and HS-621
 

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Waitaminute? :D

I just remembered that I have the schematic for the HS-442 & HS-475. See if this is one you can use.
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You're in luck! Another guy here has the exact same one. Let me dig and see if I can find his thread.

Thanks
Ive Googled and looked at everything including this site and the web for days but havent been able to get a complete picture of the entire wiring layout. I could wing it from the schematic but I like to stick with a known good layout to avoid any possible noise or feedback issues.
 
Thanks I will look at that one as well. I have a working schematic but since this thing was gutted when I got it I am trying to duplicate how they wired it. They used a combination of unused socket pins and terminals. Im trying to avoid any noise issues when I rewire it from the schematic.
 
I think I would just do away with your hand drawing. Looks like a mistake line drawn for the first 6V6 heater. They should both be pins 2 & 7.

Also if you are a novice at reading schematics, the schematic looks like it has four 12AU7 tubes but if you look closely, it shows 2 tubes split in half with different pin numbers for each half. Since the 12AU7 is a dual triode (two tubes in one bottle), this is why the schematic looks like it has wiring for two tubes instead of one. This is just one tube so I can understand how it can be confusing. :confused:

:rockon:
 
If you are interested, maybe try and find some graph paper to draw schematics on. Here is a schematic I drew from looking at the underside of a Grommes 10 watt straight power amplifier.
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Thanks! Ive been doing tube radios for a few years. This is my second amp. The first one I made from scratch it uses 2 6aq5s and a 12ax7, it sounds good but i wanted to move up to something better. I know the layout is important. I am new to amps so still learning.
I understand the schematic and how it electrically works and connects schematically . Its how they physically laid everything out Im trying to duplicate. Maybe I am overthinking it.
 
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Thanks! Ive been doing tube radios for a few years. This is my second amp. The first one I made from scratch it uses 2 6aq5s and a 12ax7, it sounds good but i wanted to move up to something better. I know the layout is important. I am new to amps so still learning.
I understand the schematic and how it electrically works and connects schematically . Its how they physically laid everything out Im trying to duplicate. Maybe I am overthinking it.
Yes, schematic conversion to actual 3D world can be confusing. The schematic does not show that parts can be wired to a lug then to a socket, or that it can be wired totally different from the schematic in terms of grounding.
My advice is to start with getting the different parts of the amp working and progressively work to completion. So, get the powersupply working first. That is make sure your AC supply, fuse, switch, is correct. Then the secondary, wire up the filament circuit correctly. Then the rectifier tube to the B+ supply with the PS caps and dropping resistors and choke. You can double check your work along the way to make sure there are no errors before moving on to another circuit. I always use a ground bus so you need to be thinking of how to lay it out because the grounds will be best if the grounded component is direcctly soldered to it. So working in sections while following the schematic from power supply to amplifier section, then to phase splitter then to input tube. If you can do it that way it may be more logical to follow the schematic..
 
OK Thanks appreciate it that sounds like good advice. I was hoping someone had rebuilt one and had a good photo on how everything was hooked up underneath from the factory . I think I will probably have to do it like you indicated. A lot of the photos I have found on this site and the web are not showing the whole picture. Connections covered up by other connections.
 
I would do what Primo said. That's the easiest. First the power supply, then the B+ circuit, then the rest.

If you make a photo copy of the schematic you are using, as you solder the wires point to point, just draw over each line of the schematic with a highlighter pen as you connect each wire in the amp.

It really doesn't matter what the amp looks like underneath as long as it is fully functional to spec then you can clean up your wiring later. I think we all do this to one degree or another. :music:
 
Yes I think thats probably the way to go. I may even do a bus wire to eliminate any grounding loops. The factory setup had multiple ground connections all over the place.
 
Going to try a bus wire this is my first one any corrections are welcome. I removed all grounds from chassis. Did an earth ground isolated next to IEC socket . Removed my RCA input next to the Volume pot It was grounded to chassis.Plan to install an isolated one in same area it was before. I will run a ground wire to the end of the bus wire. Also the bus wire is terminated only at the end next to the input. I plan to attach everything to the bus wire starting with ac and rectified power and associated caps then output tubes then 12au7s then the 6au6. My understanding is highest to lowest current draw and the input at the end. I tinned the wire. The factory setup had about 9 random chassis connections.
Not sure about what color wire to use for speaker wires on chassis from output tranny. Also what color wire to use for wire attaching to to bus wire.

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You can use any color wire you want but universally, red indicates positive and black indicates negative or ground.

No one else is going to see your wiring job unless you make a display case for it to show off after you are done. :D
 
Making progress any criticism on layout welcome. I had to do this from scratch did the best I could this is only my second build.

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Spaghetti headache. Getting a little crowded in there with the buss wire. Hope I dont have any noise issues.
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Here are some pics of my stock hs-475 chassis. I am going to convert this for guitar.
 
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How did this turn out? I have an HS-544 that I am planning on using for guitar with 4x12" AlNiCo drivers rescued from console cabinets and a Epiphone SG.

Not my first tube adventure, but I'm wondering how yours turned out and if there were any mods or issues during your project.
 
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