silvertone 6074 reel to reel conversion & topology question

[cspar]

I recently acquired a Silvertone 6074 reel to reel player to convert into an amp.

I've done a few basics just to get it going relatively close to stock.

3 prong cord, 68k grid resistor on the mic input, shorted the switch so the mic input is always live, grounded the meter so it's always on (I'll probably remove that), disconnected the tape heads and removed the motor.

It's a already a fun little single ended amp like this but I'm definitely going gut more, like the bias oscillator, pretty much rebuild it and make it an all new thing.

Searching the web it seems that folks generally convert them to Silvertone 1457's, the 3w amp in a guitar case.

I'm thinking about doing something more versatile than that. There's a decent amount of rack space without the tape mechanisms in there.

My current thought is to put in both a miniature tanked 1 tube reverb and a tremolo that can also be the lfo for a Sluckey's Warbler all tied to something akin to a Comanchero Club preamp scaled for the lower gain and frequency response of 12au7 and/or 12at7's driving a SE Rickamp.

I'm also considering puting something similar to the Li'l 4x4's vairiable compression option into it as long as I don't loose the ability to have good sensitivity and dynamics if I want it.

Perhaps this sounds like a lot to squeeze in there but I think it's doable with a bunch of planning and way easier than squeezing a flanger in a 1590LB.

I don't intend to physically work on the Silvertone other than stripping more of the tape mechanism and unnecessary parts until I've got a working prototype built on a Conn tone generator "breadboard" and a layout planned.

OK, so now that the basic backstory is there on to the big question of the topic.

The original output tube/transformer topology is something I'm not familiar with.

It seems to me that it's a current feedback thing going on that helps the tube and transformer handle both the difference in cathode biasing of the 6v6 when in different modes and the difference in output impedence between hardwired speakers and the speaker out jack.

I don't really know what's going on with it but it's something that I'd like to understand even if I never use the topology in a build.

I'm also open to suggestions about the preamp/amp to put in there. From what I previously said you can pretty much tell the direction I'm heading.

I primarily play lap steel and clean warm tone is the most important thing for me. I do however want a decent amount of gain and good breakup on tap when I want it.

I'd rather stomp any modern, doom, rock or whatever that I want to slam it with than be generally high gain by default.

I want it to function well as a clean practice amp as well as be able to push a power amp into breakup.

That's one of the advantages to me of the Comanchero Club preamp topology if I scale it correctly for less gain.

I want a versatile tone stack. I like the idea that the Comanchero Club's isn't in the signal path and it seems pretty versatile looking it over. I haven't seen the curves yet though.

My main amp is a currently a barely altered Newcomb E-17. But I have a power amp modeled after a Fender Deluxe's that is collecting dust and I'm intending to pair the conversion with it as needed.

I've worked with tubes and build a few boards worth of pedals but this will be my biggest tube project so far.

Although I want to tie a bunch of circuit blocks together I'm not trying to reinvent the wheel, just drive in luxury.

Insight on any and all of this is much appreciated.

I've attached the schematic for the Silvertone 6074 if anyone wants to take a look at that output section. The Sam's version is at Radiomuseum.org and a little more straight forward.

[sluckey]

You have great expectations for that little amp. I wonder if there's enough juice in that little PT.

[cspar]

I do, I'm looking at it as a rack to fill.

The reason that I mentioned a SE Rickamp is that I intend to add a Rickamp style power supply to supply the new section.

That would make it a amp and a Warbler/Revibe cross in a suitcase.

Using your Warbler project instead of the vibrato will make it a bit smaller as would making the reverb simpler.

Socketwise I could make it a standard Revibe as it is now and add the amp.

[cspar]

My circuit block idea is putting the "Revibe" section as an effects loop and not following nor proceeding the amp at all.

Also, removing the bottle rectifier and going solid state will make room and reduce the transformers load too.

[cspar]

Thank you for the insight Sluckey. Those few words got me pretty far.

I did some math and realized that a RickTone dual 120/12 transformer PS wasn't going to work for for my me.

Then searching around for different tube options a found Laird Bedore's site and his two different scaled down takes on the Revibe.

I could get this in there pretty easy. 

http://laird.vectorstar.com/music/effects/lesverb

Maybe with a power supply that's 120v/12v that's for the heater and one of these.

https://www.ebay.com/itm/133882043567

Then if I give the some heaters on the dry side thier own transformer I should be in lower gain, higher dissipation territory with that sides PS.

Keep the 6ax5 but put a inline fuse on it in case it shorts.

But why, oh why is that transistor strung across the OT transformer. I just don't it.

[sluckey]

But why, oh why is that transistor strung across the OT transformer. I just don't it.

What are you talking about?

[cspar]

I need to sleep I meant capacitor.

I've never seen a capacitor on a transformer like that and I don't know why it's there.

[PRR]

> I've never seen a capacitor on a transformer like that and I don't know why it's there.

All AM radios had that.

Figure 0.001uFd and say 10K impedance. About 16KHz. You don't want to hear higher than that, yet the tape deck has high gain and some strong ultrasonics.

[sluckey]

I had a Roberts Model 1057 R2R that was way more sophisticated than that cheap Silvertone. I built a simple toaster oven with it.

[PRR]

> I've never seen a capacitor on a transformer like that and I don't know why it's there.

By coincidence I learned who invented (or at least marketed) that connection.

A family/fans site. Explains this "tone control" (a cheap way to make a switched cap across the final tube plate) and how it boot-strapped the company. Robert Sprague.
https://www.spraguelegacy.com/partners
The patent:
https://patentimages.storage.googleapis.com/dd/d7/70/2b4a5b57de5a7b/US1675831.pdf

[cspar]

Wow, thanks Paul.

Neat story. And that picture of Fran playing the conga sure made me smile.

My cousin went to Hotchkiss on a scholarship. All the cabins there got officially named after Grateful Dead songs while Jerry was alive. I saw my cousins campus map back when and pointed it out to him. He didn't have a clue.

Back to the Silvertone, I haven't read the patent yet but I'm guessing that the filtering is phase cancelation.

The 6v6's cathode is connected to a resistor and then the speakers and the OT before getting to ground. That probably works into the phase cancelation too.

Not something I'm going to keep when I rebuild it.

I had a Roberts Model 1057 R2R that was way more sophisticated than that cheap Silvertone. I built a simple toaster oven with it.

Did you the cross the wires or just find it too small?

I'll take it as insight. Perhaps putting a computer fan in there would be a good thing in the end.

Hats off to you Sluckey for all the conversions you've built and designed, but I don't need the what I consider to be excessive gain and never use a overdrive channel if there is one on an amp.

I play lap steel and want to stretch out a SE amp and give it more variety but be able to get a vintage sounds too, that's the jist. The wet effects are just extra.

And I really like the form factor of the suitcase amp that the Silvertone has.

I seriously doubt if I'll have the need for anything over 20w for the remainder of my life. Plus I already have a power amp that exceeds that collecting dust as I mentioned.

Your Warbler project is one of the coolest tube projects I've seen. I've been intrigued by it for a few years now. It's really the Liquidator version that  intrigues me the most.

The only reason that I haven't built one is that I haven't found a saturatable reactor yet and I'm not willing to pay the prices I see on ebay. So I'm looking on Craigslist and curbs until one comes my way.

The 6074 isn't my only reel to reel. I have an Akia 345 collecting dust because I don't have the skill and knowledge yet to make a tape delay out of it.

I also have a Silvertone 4236. It seems that I need to buy the Sam's if I want the schematic for. It has more of a crunchy modern sound to it.

It's a 2 headed dual channel but only one channel at a time. Record mono, play stereo. I've only ever used the one channel.

6av6, 6eu7 and 6em7a for each channel.

I've even got a widowmaker RCA 400 junior projector that I like the tone of through an isolated input. I can't find a schematic for the junior and haven't traced it yet to try to find out why I like it. It's gathering dust.

Now that I have a bunch of experience building pedals mostly on perf, done a bit of tinkering and moding with tubes and gathered more testing equipment I'm ready for this bigger project that is really two project.

The point to point amp and the tagboard wet side.

Over 99% planning is the way to go.

Although it definitely isn't going to be as glorious as your journey through Hammond conversions I feel that I'm at the start of my own journey through some single ended conversions.

Obviously there is a lot that I don't understand and tons that I need to learn but I'm on the path.

I took my time writing this out because I tend to communicate with a autistic stream of consciousness flow that sometimes people have a hard time with. It's a part of who I am.

I can understand how that might not be conducive at times within a high voltage forum and will try to make my posts here as clear as possible forthcoming.

I'm ok with you guy's changing my user ID to ramblingfreak so there is forwarning.

[PRR]

> cabins there got officially named after Grateful Dead songs

[sluckey]

The only reason that I haven't built one is that I haven't found a saturatable reactor yet and I'm not willing to pay the prices I see on ebay. So I'm looking on Craigslist and curbs until one comes my way.

I can sell you an AO-47 cheaper than you will find on eBay.

[cspar]

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