Magnatone Twilighter 2020--MOD BUILD-Only Tremolo

[sluckey]

I think the schematic/layout file is correct. Destroy all previous versions. LMK if you spot any errors or have questions.

[wsscott]

Thanks so much.  Will do.

One question, I think you said you put in the brightness option, so is that some kind of a separate SPST toggle switch of some sort, or is it a push/pull 1 M-A pot of some sort?

I was thinking I might add to the length of the board a bit and install some extra turrets in case I wanted to come back later and add a reverb. I'd also include an extra tube socket, and related mods to the chassis. If I did want to add a reverb, would you add the tube reverb circuit from the M10A mod that I did, or the one from this Mag Twilighter circuit or the one from the Hoffman Deluxe Reverb circuit?

[sluckey]

One question, I think you said you put in the brightness option, so is that some kind of a separate SPST toggle switch of some sort, or is it a push/pull 1 M-A pot of some sort?

Look at the schematic and layout.

I was thinking I might add to the length of the board a bit and install some extra turrets in case I wanted to come back later and add a reverb. I'd also include an extra tube socket, and related mods to the chassis. If I did want to add a reverb, would you add the tube reverb circuit from the M10A mod that I did, or the one from this Mag Twilighter circuit or the one from the Hoffman Deluxe Reverb circuit?

Use the Twilighter one tube reverb and put it on the preamp end of the board.

[wsscott]

Thanks.

[wsscott]

Sluckey- In the Layout section, pre-amp section, it looks like you're showing .0047uf caps instead of .047uf as shown on the schematic. 

The layout shows a .022uf cap connecting to the grid of V2 and I think it should be a .0022uf based on the schematic. 

The 82K R coming off of V2-Pin 6 should be going to B, but appears to be going to C node or is the 10K 3W R blocking it going to C and thus its at B node? 

What does "NFB" mean on the External Speaker Jack?

I don't see the .01uf 2KV Cap between the Standby at the Choke and the OT.

A minor point, but some of the tubes on the schematic are mis-labeled, ie. they still show their original designation from the original schematic:  See V4 & V5 mis-labeled as "V6" and "V7"; V3 mis-labeled as "V5-A".

I may have misinterpreted the Layout, and sorry if I screwed up with these comments.

[sluckey]

Sluckey- In the Layout section, pre-amp section, it looks like you're showing .0047uf caps instead of .047uf as shown on the schematic.  fixed 

The layout shows a .022uf cap connecting to the grid of V2 and I think it should be a .0022uf based on the schematic.  fixed

The 82K R coming off of V2-Pin 6 should be going to B, but appears to be going to C node or is the 10K 3W R blocking it going to C and thus its at B node? There is no 82K coming off of V2-6. Both V2 plates correctly connect to Node B.

What does "NFB" mean on the External Speaker Jack? NFB = negative feedback

I don't see the .01uf 2KV Cap between the Standby at the Choke and the OT.  fixed

A minor point, but some of the tubes on the schematic are mis-labeled, ie. they still show their original designation from the original schematic:  See V4 & V5 mis-labeled as "V6" and "V7"; V3 mis-labeled as "V5-A".  fixed

THX for catching those errors. LMK if you spot others. I'm uploading the fixed file into post #50. Please delete the old one.

[wsscott]

Thanks

[wsscott]

Yes, I meant "plates" but said "grids" and should have referred to V-2 Pin 1 not Pin 6.  Sorry, sloppy of me.

[sluckey]

Hey, we're getting it fine tuned. Keep on looking.   

[wsscott]

Will do.

[wsscott]

I've been looking for output transformers, and of course Classic Tone is out of business and they're hard to find.  Also, some of the Hammonds are out of stock.  I did find a Hammond 1760H available, and have attached the data sheet, and wanted to know if you think this would be a good fit.  I really don't need the flexibility of 4 and 16 ohms, but its there.  Any other choices you recommend?

[wsscott]

Or this Hammond 1760J?

[wsscott]

Sluckey-I've compared the original Twilighter circuit from Magnatone with your Visio schematic 2 times, and it matches up.  I also have gone over your revised Layout 2 times and compared it to your Visio version of the schematic and they match up.  So looks to me like this version is good to go.

Three more questions about components.

As to the brightness, push-pull, pot, I've looked around for the pot and I've seen comments about one particular brand being poorly built. Is there one that you would recommend?  Alternatively, is there a different kind of switch, like a toggle switch I could use instead.  Would it be a SPST or DPST? In fact I probably would prefer that.  Recommendations?

Then as to the Bias Trim pot, I've got one on order that looks like a typical 3 terminal pot, made by Alpha, and it can be mounted to the chassis like a regular pot.  Access to the adjustment screw slot would be on the outside of the chassis.  Any reason not to use it? Is it really inconvenient to be adjusting it from the outside of the chassis vs. inside the chassis?

Finally, the way I'm planning on designing the chassis is to have it similar in design to the Mag. Twilighter chassis.  The Layout has the tubes located on the opposite side of the turret board from the pots.  In my design though, that would put the tubes way back into the cabinet near the speaker.  So I would want to move them towards the front of the chassis so that they are visible and accessible from the rear of the cabinet.  If I move them to the front side of the turret board in the chassis, that would work, but would it affect the wiring or circuity in any way?  I assume not.  I would just be running the hookup wire under the turret board to the front of the chassis instead of to the rear as is in the Layout.  Any thoughts on this placement issue?

Thanks. 

[sluckey]

1. You can use any kind of switch. Just mount it close to the VOL pot. This is the pot/switch I use for a bright switch...

   https://www.tubesandmore.com/products/potentiometer-cts-audio-1-m-spst-push-pull-solder-lug

2. I would not use a bias pot with a shaft unless you get an expensive pot with a locknut to prevent accidental turning! Hoffman sells a CTS 10kl Fender Bias Pot that is chassis mount but can be adjusted only with a screwdriver from either side of the chassis. Very handy and safe. My board was designed to use the onboard bias trimmer pot that Hoffman sells.

3. You can layout the chassis any way you want, but... My board layout was designed to work together with the tube placement and control panel. If you deviate much from my layout you probably should redesign the board too.

[sluckey]

I've tweaked the board layout slightly. Much neater bias section. The updated file is in post #50. Please destroy previous versions.

This is my final tweak unless you discover any more errors.

[wsscott]

Thanks again.

[wsscott]

Any thoughts on the Output Transformer?

[shooter]

as long as the OT meets current requirements and basic 0 to ~~ 8khz they all work.  The speaker is where you want to fret

[sluckey]

Any thoughts on the Output Transformer?

At some point you mentioned 15 watts. If that's what you want then use a Princeton Reverb PT and OT. If you want 22 watts then use a Deluxe Reverb PT and OT. Since Magnatone borrowed the DR circuit from Fender, I'd just use all DR iron,,, PT, OT, and choke.

[wsscott]

I don't intend to change the Layout of the turret board.  It looks great and is accurate. 

In order to get the tubes on the front end of the chassis, ie. opposite to where they are now, what if I just turn the turret board, and the pots, etc., 180 degrees when I install it.  Then I could put the tubes on the front end along with where the pots are?  Any issues with tube socket proximity to pots and input jacks?

[sluckey]

what if I just turn the turret board, and the pots, etc., 180 degrees when I install it.

That put's the sensitive inputs and preamp on the PT end of the chassis. You'd be better off just to slide all the tubes to the top of the layout. Wiring will not be optimized nor as neat.

Why do you want to do this? This stripped down amp is 95% Fender and only 5% Magnatone. Had I known you wanted tubes on the control side I would have laid out the board to accommodate.

[wsscott]

I meant I would just switch the entire physical layout around, not just the board.  So the PT and related components would be flipped.  I want to do it like this because I want the control panel to be on the backside of the amp, and not the front like the blackface Fender's etc.  I want the front of the amp just to be grill cloth.  So your layout is fine, I'm just trying to humor myself with the clean look I like with amps from the front.

[sluckey]

Just slide all the tubes and cap can to the top. And slide the board, PT, and choke down.

[sluckey]

This seems to be what you have in mind. Will you also bring all that stuff from the bottom up to the control panel?

[wsscott]

Yes, that's the idea.  The power and standby switches, and the Line Out and Remote Speaker jacks would be on the front panel, and the rest would be on the bottom of the chassis but up front towards the control panel. The IEC and fuse will be on the bottom of the chassis in the front with everything else.

I assumed though, that I should flip the Turret Board 180 degrees so that the connections from the board to the tube sockets would be short, and if I did that then I'd need to put the PT and the OT on the other end too in order to keep it away from the pre-amp.

[wsscott]

Sluckey-does your software generate a BOM?  I'm working on one in Excel, but I'm not very good with sorting the data.  Don't fool with it if your software can't generate it.

[sluckey]

Don't rotate the board! Just flip it over after drilling and install the turrets on what used to be the bottom. Should look like the attached. You can make this layout or something similar work. Wiring may look messy in some spots but may look better in others.

I don't do BOMs. All the small components can be found at Hoffman. AES, and Mouser. Iron and cap can from AES. No one has everything you'll need. Some of the oddball caps I found at Mouser.

[wsscott]

Great.  Thanks.

[wsscott]

I had a question about the signal path through the Treble Boost/Bright part of the circuit. 

Am I correct that the signal comes out stage 1 of the pre-amp thru the Treble pot, and then heads into the Volume pot where it splits going into that pot.  The main part of the signal goes through the Volume pot at ALL times, but if the DPST switch is in the ON position, part of the signal is diverted and goes through the 120pf cap to the Output of that pot so that it mixes with the signal going to the grid of stage 2 of the 12AX7.

Am asking because I've decided to use a toggle switch, DPST I believe, rather than the push-pull pot, and want to be sure how I wire it up.  Thanks.

[sluckey]

The bright switch allows high frequencies to bypass the resistance of the volume pot. That's what makes it a bright switch. At full volume it is shorted out and does nothing. I used a toggle for bright on my TDR which is the same as your amp except I opted to have reverb rather than tremolo. Fender used a slide switch. I later turned to the switch/pot just for it's one hole simplicity.

[wsscott]

Am I correct that a DPST switch is the proper type?

[sluckey]

Am I correct that a DPST switch is the proper type?

Any switch will work. Your DPDT will work but you are only gonna use two contacts. In fact, Fender used a DPDT slide switch even though he only used two contacts. SPST is all that's needed.

[wsscott]

Thanks.

[wsscott]

I was watching a YouTube video today comparing a Deluxe Reverb with a Princeton Reverb, and the guy was commenting that the DR in the Vibrato Channel is extremely loud and piercing even at low levels because of the Bright Cap on the Input for that Channel.  He was saying that even at low settings, like 3, which is at the volume level you would want in order to get the clean sound, its extremely loud.  He was talking about ways to get the volume level down to a home or recording studio level but still maintaining the tone. 

I would think that the circuit Sluckey came up with, that the issue is really moot because you can turn off the Bright effect.  Thoughts?

[sluckey]

and the guy was commenting that the DR in the Vibrato Channel is extremely loud and piercing even at low levels because of the Bright Cap on the Input for that Channel.

That's bullshit. The reason the DR is louder than the PR is because the PR's PI has no gain and the DR's PI has lots of gain. However, I know how to play a DR just as quietly as a PR.   

Your amp will be louder than a PR too, with or without the bright cap.

[wsscott]

Yes, there are a lot of know it all on YouTube and a lot of them are full of BS.  Since I've never played or even hear a DR, what do you do to get the sound you like at listening level/comfortable volumes?

[shooter]

the sound you like

that's like askin boxers or briefs 
the soldering pencil isn't even hot, you're getting ahead of yourself 

[wsscott]

I would have been a good Boy Scout: Be Prepared! Haha!

Speaking of soldering, what temp do you guys normally run?  I normally run at 790 degrees, and wondered if that’s too hot. Thanks.

[sluckey]

what do you do to get the sound you like at listening level/comfortable volumes?

I turn the volume down.

[shooter]

Be Prepared! Haha!

Nixon signed my Eagle Scout card 
One of the better axioms for life

[acheld]

I solder @ 700F.

[wsscott]

Sluckey, what’s the angle for the Mag chassis? It looks about 45 degrees. I’m waiting for parts to arrive, so I thought I would figure out the chassis dimensions and details so I can contact a cabinet source. Guitar Cabinets Direct did the cabinet for me before and did a great job, and did some minor mods that weren’t expensive. Thanks.

[sluckey]

No idea.

[wsscott]

I got the parts and have started installing them on the turret board.  I'm using the original configuration you did Sluckey.  I've decided not to "reverse" everything and just install the chassis so its like a standard Blackface.

Issue, I ordered a 220uf 25V cap that goes in the tremolo circuit coming off the cathode on V3 along with the 3.3K resistor.  Your layout specifies 35V.  Will the 25V that I got work without the risk of blowing, or should I order a 35V cap?  Thanks.

[sluckey]

Look at the original schematic.

[wsscott]

Ok, it calls for a 10V, I guess you just added some extra protection, so my 25V should be fine.

[wsscott]

Now, if I had just bought some 82K ohm resistors instead of the 82 ohm resistors that I in fact purchased, the turret board would be complete. I've got 68K ohms and 100K ohms resistors, but do I have an 82K ohm resistor.  No. But Oh NOOOOOO, I couldn't have gotten it right the first time.  So I guess that will wait until I order some tubes or something else in order to justify the shipping!

[sluckey]

Ok, it calls for a 10V, I guess you just added some extra protection, so my 25V should be fine.

I couldn't find a 22u/10v radial at my main suppliers so I bumped the voltage rating up a bit. Besides, I already had a stencil for the 35V cap.   

Now, if I had just bought some 82K ohm resistors

Get a 5-pack. That's a very common resistor for Fender amps.

Could you post a pic of your board? I'm curious about the fit of that big ole .68µF. I have never held one to do my actual measurements. Just had to trust AES's numbers.

[wsscott]

Attached is the turret board.  The .68 cap fit perfectly.  The turrets you see that aren't connected are for future use if I decide to add in the reverb.  Also, because I added those turrets I had to go under-board to be able to connect the .0022uf cap to the 1M ohm resistor.

[sluckey]

You used two .68uf/100v! That 100v cap will probably work for the cap that is labeled .68uf/250v. But the ***BIG*** .68uf that has no voltage listed on my layout must be at least 500V rating. Your 100v cap will quickly fail.