Help with Silvertone 1449/1457 amp layout

[keedba65]

Hi!
I'm kind of new to this forum, but I have been on TDPRI for some time posting about building tube amps.

I'm thinking about building a Silvertone 1449/1457 amp (head format). I prefer circuit board layout to point-to-point wiring so I want to do it with a circuit board. Trouble is, there is no circuit board layout that I have been able to find so I did it myself.
Here is the schematic for the Amp (from a scan of an owners manual):

Here is the parts list (from the same scan):

and here is my attempt at layout:

I have omitted the power supply wiring and output transformer wiring. Also I am planning to use Switchcraft type jacks, not Cliff (pictured) but I didn't want to create a part for the Switchcraft 12A/B that are used so the ground connections on the jacks will connect.

For power transformer I plan to use the Hammond 269JX 250-0-250 60mA. This should be sufficient but I would like advice there as well.
For output transformer I plan to use one suitable for a Fender Champ (the P-T31 from Tubes And More, 8W, 5K primary, 8 Ohm secondary).

I am not happy with the rats-nest crisscross between the pre-amp 12AX7 and vibrato 12AX7 so help there would be nice.

I know that the black face vibro champ has the same features, but I want something different and the Silvertone seems like a good choice.

Thanks for your help!

[sluckey]

The layout has a few errors in the trem circuit. Look closely.

[keedba65]

The layout has a few errors in the trem circuit. Look closely.

Thanks Sluckey,
I see that pins 1 & 3 on the tremolo tube are swapped.  I don't see any other issues so if there are I need another hint.

I am worried about all the crisscross between the pre-amp tube and tremolo tube wires, particularly power, though it is on the less sensitive (2nd stage pre-amp) side of the pre-amp tube.

[sluckey]

I'll play with it a bit. You don't really have to use that perf board do you?

[2deaf]

While you're waiting for Sluckey.  Probably some errors, but you can sorta see the general idea.

[keedba65]

I'll play with it a bit. You don't really have to use that perf board do you?

Hi Sluckey,
Thanks for the help!
No I don't have to use that perf board, it's just convenient.

[keedba65]

While you're waiting for Sluckey.  Probably some errors, but you can sorta see the general idea.

Hi 2Def,
Thanks!  It looks cleaner, I will have to highlight it and check it against the schematic.  Most of my experience is with Fender layouts so it is Fender like.
Thanks again!

[keedba65]

Updated layout (my original with vibrato tube wires corrected)


Layout based on drawing provided by 2Deaf

I still haven't got out a highlighter and verified it but this one looks pretty good!  Thanks 2Deaf.
Note: I noticed that in 2Deaf's drawing the vibrato tube was inverted.  I considered this but rejected it because it would put the filament wires on the opposite side from the other tubes and I like to run the filaments close to the chassis. - Maybe I am wrong here?
Anyway Thanks 2Deaf!

[Platefire]

Hi Keedba65

Glad to see you posted you project here and Welcome! Looking forward to following your project. Platefire

[2deaf]

Note: I noticed that in 2Deaf's drawing the vibrato tube was inverted.  I considered this but rejected it because it would put the filament wires on the opposite side from the other tubes and I like to run the filaments close to the chassis.

I don't really understand this inversion.  I didn't include the heater pins, so the tube can be mounted with the filaments in either orientation.

The vibrato tube is not connected properly.

The placement of the wires was given some consideration in order to minimize the possibility of parasitic oscillation.

[keedba65]

Note: I noticed that in 2Deaf's drawing the vibrato tube was inverted.  I considered this but rejected it because it would put the filament wires on the opposite side from the other tubes and I like to run the filaments close to the chassis.

I don't really understand this inversion.  I didn't include the heater pins, so the tube can be mounted with the filaments in either orientation.

The vibrato tube is not connected properly.

The placement of the wires was given some consideration in order to minimize the possibility of parasitic oscillation.

My mistake: It looked inverted to me.  You swapped v2a and v2b, but I was still looking at it as though v2a and v2b were as specified on the schematic, but the tube rotated 180 degrees.
I get the idea of minimizing the possibility of parasitic oscillation.
When I get a chance I will update my drawing. 

[keedba65]

Updated layout based on 2Deaf's drawing.

[sluckey]

This is what I've been working on. I still need to 'proof' it before posting a pdf version. I lined the tubes up the way Sears did. If this interests you I'll finish up later tonight or early tomorrow. My multipage pdf will include pics of the actuall amp, schematic, actual size layout, and a full size drill guide that will make it easy to make your board (or you can hand it off to Hoffman and he can make you a CNC board).

[kagliostro]

Steve

Ogni volta che vedo un tuo layout resto a bocca aperta

Franco

[2deaf]

This is what I've been working on.

I like it.  Good idea reversing the tone control.

[keedba65]

This is what I've been working on. I still need to 'proof' it before posting a pdf version. I lined the tubes up the way Sears did. If this interests you I'll finish up later tonight or early tomorrow. My multipage pdf will include pics of the actuall amp, schematic, actual size layout, and a full size drill guide that will make it easy to make your board (or you can hand it off to Hoffman and he can make you a CNC board).

WOW! This is a significant work product, including research on the Sears guitar case amp the circuit is from!
I like the layout.  It is very clean and looks well optimized.

Thanks for the effort!
Kevin

[sluckey]

Here's the final. The file is too large to attach here so I'll just provide a link. Let me know when you get it. Nothing lasts forever...

     http://sluckeyamps.com/misc/Silvertone_1449.pdf

[Platefire]

Great Work sluckey! This may be the first time that this Silvertone circuit has been put into a revised
updated format---ground breaking!!!

[keedba65]

Yes! Excellent work!  Thank you Sluckey!
Anybody got a comment or recommendation about the power supply?
I was thinking about using the Hammond 269JX 250-0-250 60mA.
I want to have the B+ voltage come in close to the specified 330v at the first filter cap. I used Tube Amp Power Transformer Current Draw Calculator to compute the expected voltage and current draw (for 2 pre-amp and 1 power tubes, SE, diode rectification) and the 250-0-250 comes in at 342.5v and 54.38mA current draw. The Hammond 269JX should be able to handle that since it is rated at 60mA and I am guessing that the 12AX7 used as a vibrato will use less current than it would as a pre-amp tube (the calculation is based on all pre-amp tubes being pre-amp).

[sluckey]

The Hammond 269JX is a good choice.

[keedba65]

Cool, Thanks Sluckey!

[purpletele]

What a nice surprise!

That should help you get going!

[kagliostro]

I'm not so skilled, so ....

Datasheet say 8.5K Load for 315V B+

http://www.mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf

with the planned ~340V B+ which will be the right load ? 9.5K ??

Franco

[sluckey]

keedba65, I'm curious as to why you chose to build this amp. It's such a low end, unremarkable amp that I just don't see the attraction. I can totally understand restoring one of these from a nostalgia standpoint if you have the guitar and case/amp. This complete rig sold for $99.95 new (could probably be had for $79.95 in the Christmas catalog). But when you take the amp out of the case, you're left with a really cheap, very low end consumer product.

I've see quite a few restored Silvertone amps, usually the larger ones, and I know that in recent years they have become popular, although I don't get it. My first real amp was the Silvertone 1484 "Twin Twelve" because, like so many other Sears customers, that was the only big/loud amp I could afford. So, please tell me, what's your attraction to this amp?

[keedba65]

Hi Sluckey,

This is mostly a learning exercise for me.  I wanted to get some practice and learn about circuit layout.  If I just wanted to build the amp, I could have used the pictures and done a point-to-point implementation, just like the originals.  If I just wanted a 5 watt amp with vibrato, the Vibro Champ is available.

I am a software engineer by trade.  I am also quite interested in electronics, though I have had trouble with some of the concepts - I really need to observe them to get them.  I used to work in EDA software - back end - I understand photo-plotters and PCB manufacturing basics.  In this capacity I got to know a few designers and came to understand that layout was sometimes as much art as science.  For example, at that time, although auto-routers were mature and common, almost no PCB was completely auto-routed.  Almost all needed the routing to be finished by an experienced designer.

I have already become comfortable with the building process, doing clean component connections, soldering, planning, etc. with circuits that have already been laid out and those layouts time tested.  I came across this circuit, looking at some of the classic Silvertone equipment, and I thought I could do this, I could lay it out.
It had not been done before, that I could find.
It had a basic circuit that I could start from.
It had a tremolo circuit, so I could learn that as well.

I know it is a very low end consumer product - but then again so is the Fender Champ.

It has been very helpful seeing the work product from a very experienced designer.  I can already see several places where I made mistakes in layout and have learned quite a lot from it.
Thank you so much for your help!

[keedba65]

I'm not so skilled, so ....

Datasheet say 8.5K Load for 315V B+

http://www.mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf

with the planned ~340V B+ which will be the right load ? 9.5K ??

Franco

Hi Franco,
I'm not very skilled at this either, however, the output transformer I want to use is intended for the Fender 5F1 champ circuit:

As you can see, the B+ is 340V.  I have seen both 5K and 7K or 8K taps specified for 5F1 type circuits.
If it is recommended, I can change to use an output transformer in the higher impedance range.  In any case, I feel that an output transformer aimed at a 5F1 circuit should work for this project.
Thanks for your help!
Kevin

[sluckey]

I hope I didn't sound like I was trying to discourage you from building this. That was not my intent. I just wanted to know what attracted you to this particular amp. I thought you may have owned a 1449 as a kid or had heard one at sometime and really liked it. I've never known of anyone that built a Silvertone before. Your reasons make perfect sense. I hope you build this and will share your project with the forum.

[PRR]

If you are going to make a million to put in large store showrooms, you may need to "optimize" the load so it impresses the customers. (However the speaker will be more difference than another Watt.)

IIRC, Epi Valve Jr uses 7.5K or 8.5K to suit their high B+ (and EL84). They probably did the testing and got that numbers, for their goals, for the speaker they had in mind.

5K and 7K are readily available Champ-ish OTs. Use whichever is closer to your hand.

[sluckey]

I'll bet Sears spent way more time designing this amp to physically fit in a guitar case than they did 'optimizing' the circuit to be electronically correct.

[kagliostro]

I've seen 7K - 3.2ohm OT for Champ (Hammond 1750C)

https://www.tube-town.net/ttstore/Transformer/Outputtransformer/Fender/Hammond-1750C-Fender-Output-125A35A-022905-Champ::2200.html

if you connect a 4ohm speaker the reflected impedence rises to 8750ohm

and seems to be near the right impedance with 340V B+

Franco

[keedba65]

I hope I didn't sound like I was trying to discourage you from building this. That was not my intent. I just wanted to know what attracted you to this particular amp. I thought you may have owned a 1449 as a kid or had heard one at sometime and really liked it. I've never known of anyone that built a Silvertone before. Your reasons make perfect sense. I hope you build this and will share your project with the forum.

Don't worry, I didn't take your question as trying to discourage me.
I plan on moving forward with this project and I will share my progress on this site.
Next steps: review my BOM and kit the parts I have so I can order the parts I don't, order board and turret material, drill and set turrets.
Thanks for all the help!

[PRR]

> I've seen 7K - 3.2ohm OT for Champ

Stock Champ was usually "7K" primary.

This comes from using parts for a 6V6 radio (5K OT) with field-coil speaker, but omitting the FC, which gives a higher B+ at the tube. As Fender was more power-hungry than most radio makers, he left the current almost as high and let the 6V6 run hot.

The difference "3.2" or "4" is really almost no difference. Before RMA speaker test standard, we often went by DC resistance. When tested in the 250Hz-500Hz area, a 3.2 Ohm DCR coil will act like near 4 Ohms. They are the same speaker. While this does calculate to a different primary impedance, the difference is small, overwhelmed by loudspeaker variation.

[kagliostro]

Ciao PRR

Stock Champ was usually "7K" primary.

This comes from using parts for a 6V6 radio (5K OT) with field-coil speaker, but omitting the FC, which gives a higher B+ at the tube. As Fender was more power-hungry than most radio makers, he left the current almost as high and let the 6V6 run hot.

I love this explanations you often give us about old gear, THANKS

--

..... the difference is small, overwhelmed by loudspeaker variation.

Yes, I agree, but this variation is on also if you connect a 3.2ohm speaker to a 3.2 ohm tap or a 4ohm speaker to a 4 ohm tap, so the different reflected impedance using a 4ohm speaker is real, am I wrong ?

Franco

[keedba65]

I decided to try Sluckey's layout - it seems a bit cleaner than mine or 2Deaf's.
Here are some pictures of my progress.
Board, template, turrets


Template taped to booard


Holes marked with punch


Holes drilled


Setting turrets


Turrets set

[sluckey]

I have a couple board tips...

Installing turrets. Mount the cone shaped part of the turret press to the drill press table and put the other part in the drill chuck. Then you can load all the turrets in the board and press them all at once. The turrets will be 'right side up' so they won't fall out. This greatly speeds up the process. I like to put my head at eyeball level with the board so I can see above and below. At first it may seem that you are blindly flaring the turrets but you will soon get a feel for when the turret is properly positioned on the cone.

I probably would not put any under-board jumpers on this board. But when I do use them I want to know they will stay in place securely. So, I always push the end of the jumper completely through the turret and 'hook' the end back over the outside of the turret. This little detail allows you to see the jumper even after soldering, but more important, it prevents the jumper from falling out of the turret whenever you do any later soldering. I use 22awg jumpers and that leaves plenty of room for component leads.

[keedba65]

Thanks for the board building pro tips Steve!
The turret setting tool and procedure are from a TubeDepot kit so I was just following those instructions.  It does make sense to invert the tool so the cone is on the bottom.  Also a valuable tip under board jumpers.  This layout does call for 3, however they can also be placed above without much trouble.

I see you have two kinds of above board jumpers in your picture, those with insulation and those without.
What determines which you use?

Thanks again for all the help!
Kevin

[sluckey]

I see you have two kinds of above board jumpers in your picture, those with insulation and those without.
What determines which you use?

The insulated jumpers will be connected to a B+ node.

[sluckey]

The Library of information link at the bottom of this page contains a lot of helpful info. Here's Hoffman's video showing how he installs turrets...

https://www.youtube.com/watch?v=bpVai-RajFM

[keedba65]

I had some time to make more progress on the circuit board.  I have some parts coming so it may be a while before I can start with the chassis work.
I added the jumpers to the top of the board


And added a few jumpers to the back of the board as well


I usually solder the wires leading to off board components (jacks, pots, sockets, etc.) after the board is populated, however with this board there were many wires that lead to inner board turrets so i drilled and wired them before I add components


Another view with more of the board design page showing

[PRR]

Images not visible. They may not be set "Public"? They may not be images but web-pages with images?

[sluckey]

They were visible earlier today. Something has changed. 

[keedba65]

I just refreshed the images - I didn't change anything in Google Photos, but the copied URL's are different, weird!