toneking imperial voltages / transformers

[sluckey]

Duh huh.   

Now let me make a couple suggestions. Drop the two resistors. They're not needed. Remove the reference to H1 and H2 since this is a dedicated transformer used ***ONLY*** for the relays.

Seems you want K1 and K2 energized at the same time? So simply connect the two coils together (parallel). Don't loop the voltage through K1 contacts. While that will work, it's a bit klutzy.

[sluckey]

What is the coil voltage of your relays? If 5V, I suggest using a 7805 VR chip.

[Bieworm]

thx!!
well..did you see the last post where I dropped the hoffman schematic and reintroduced the Imperial schematic? I seem to understand now what its says..
your post referred to the imperial schematic, or the hoffman?

I ordered a few things whil ordering the parts for my amp.
I found a 6V power supply kitthat should work for juicing the relays
I also ordered a 6V double relay switcher kit with stereo cliff jack and diodes,... included. I want to use that for 1 relay for the tremolo and the other for the channel switching. I also ordered a separate relay for the 2nd one on the channel switching. With those it's just a matter of figuring out the connections and I should be set.
For safety I ordered a few relays extra in case I have to follow my first plan. Also the diodes and 4700uf cap...

here are the links to the relay stuff I ordered

https://www.tube-town.net/ttstore/finder-relays-dpdt-125v-2a-6v.html

https://www.tube-town.net/ttstore/tt-kit-extra-power-supply-6-v.html

https://www.tube-town.net/ttstore/kit-double-relais-switcher-6-v.html

[sluckey]

your post referred to the imperial schematic, or the hoffman?

What I said applies equally to either schematic.

[Bieworm]

I'm figuring out a layout for the amp. I've prepared the turretboard for the preamp and the filtercaps.
The reverb tx is to be built in that location underneath the chassis ofcourse. The location of the PTX, choke and OTX will be placed just like the DR. Is there anything in the layout that is going to give trouble for sure? What should I change?

[Bieworm]

I thought of a new chassis layout. The blue cube is the relays power supply. I think of running the wires to the relays under the top corner of the backside and the heater wiring along the low corner of the backside. Maybe the rectifier tube should be in the front corner under the pilot light?

[Bieworm]

The build is ready (amp chassis) and it sounds awesome!!!

https://www.dropbox.com/s/k7pm8migiki1fq4/Imperial%20build%20first%20recordings.m4a?dl=0

[Bieworm]

99% finished. A few hardware stuff and the reverb bag ( have to beg my wife to get behind het sewing machine)

[Bieworm]

Is there any hazard involved with the
 Hoffman 1/4 power switch with resistors? I mean that on running the amp halfway.. not full throttle

Bump

[Bieworm]

another thing I think is incorrect about the imperial schematic. It connects the screen grid to B3, which is only about 350V. It think it'd be better to downsize the resistor between B2 and B3 so I can raise that to 410V. Maybe I should try swapping R87 en R88's values so there is 5k between B2 and B3 / 10k between B3 and B4. That seems to make more sense to me.
Sad thing is I don't have any reference voltages for the imperial besides the 5E3 and BFDR voltages. the schematics of these are pretty similar to the imperial preamps. The PI is very different.
It would also make more sense to have a higher voltage on B3 for the reverb because the BF reverb has also got 410V on the plates of the send half and 170V on the platse of the recovery half.

anyway, the difference of +-80V between plate and screen on those 6V6's don't seem right...
and I think I will also try out what the effect of a bypass cap on the cathode from V1 will bring. There is none on the schematic, but maybe it's better with one? Both the 5E3 and the BFDR have one. OTOH it might be overkill for the OD channel, which shares that first preamp stage...

[sluckey]

Is there any hazard involved with the Hoffman 1/4 power switch with resistors?

What's the Hoffman 1/4 power switch? Can you provide a pic or a link?

another thing I think is incorrect about the imperial schematic. It connects the screen grid to B3, which is only about 350V.

I doubt that is a mistake. It's a good thing.

Maybe I should try swapping R87 en R88's values so there is 5k between B2 and B3 / 10k between B3 and B4.

That's how it is now. I'd let it be.

[Bieworm]

Oops.. it has to be robrob
https://robrobinette.com/Generic_Tube_Amp_Mods.htm#Quarter_Power_Switch

Towards the B3.. I was just worried the voltage difference between the screen and the plates on the 6v6 was too large. The 5E3 and BFDR don't have that big difference.. don't want to ruin good new tubes

[Bieworm]

+ I found it odd the schematic calls for a 250R cathode resistor.. but to get the bias at 85% range I had to put in 400R. With the 250R it was 113%

[sluckey]

That quarter power switch should work just fine.

+ I found it odd the schematic calls for a 250R cathode resistor.. but to get the bias at 85% range I had to put in 400R. With the 250R it was 113%

250Ω is the standard value used for P/P 6V6s. Cathode biased amps typically run at 100% or more. Not gonna hurt anything to increase the resistor value.

[Bieworm]

Thanks

[sluckey]

Towards the B3.. I was just worried the voltage difference between the screen and the plates on the 6v6 was too large. The 5E3 and BFDR don't have that big difference.. don't want to ruin good new tubes

That voltage difference is not too large. Your new tubes will last much longer with the reduced screen voltage.

Fender and many other manufacturers run the screen at or near the plate voltage to squeeze out every bit of power they can. Doing so is hard on the tubes.

Heck, some of the big bottles, 6550, KT88, etc., run the plates at 600V and the screens at 300V.

[Bieworm]

Well.. I tinkered around with some stuff and I think it's fatter and greasier sounding.

1. I put a B500k pot in series with R21, the last resistor of the drive channel right before the input of the PI circuit. By raising the resistance I can get the OD at a little less volume.
2. I put a 47uf 63V cathode bypass cap parallel with the 820R (R3) on V1. This beefs up the tone and makes it somewhat greasier.

Is there any harm in doing those mods?

[philipdfisher]

Bieworm, I realise this is an old post but just wanting to ask if you found the mid-bite channel anemic at first ... in your last post you said you put in some mods?  I have just completed the build myself; I've put in a reverb similar to the Princeton and the bias wiggle circuit similar to the Ampeg J12B.  Everything sounds great apart from the first channel - it hasn't got much bass and the mid bite isn't particularly effective.  All voltages I have recorded are very similar to what you posted.  If you get this then I can post my layout to see if there are any differences.

[Bieworm]

Bieworm, I realise this is an old post but just wanting to ask if you found the mid-bite channel anemic at first ... in your last post you said you put in some mods?  I have just completed the build myself; I've put in a reverb similar to the Princeton and the bias wiggle circuit similar to the Ampeg J12B.  Everything sounds great apart from the first channel - it hasn't got much bass and the mid bite isn't particularly effective.  All voltages I have recorded are very similar to what you posted.  If you get this then I can post my layout to see if there are any differences.

While the standard TK imperial OD channel is fun, it would never be useable Iin a band setting. + the volume is close to uncontrollable if you want OD.
I did indeed do a lot of tweaking to that channel ending up with abrown medium OD marshall tone. Very nice! It also involved changing the paraphase PI into LTP PI... much more control over the volume overall.
Ignore that last post. I changed values since then...

Look at the schematic attached. Note that the 220k resistor circled in blue has landed on  100k. 220k took too much signal away, and no resistor at all made the clean channel interact too much with the OD channel.
Sound clip.. crappy phone recording
https://www.dropbox.com/s/4ztce46vyo1e8n7/Rockinbird%20full%20blast.m4a?dl=0

Please post some pics of your build. I wanna look at how you've done things..

[philipdfisher]

Thanks for coming back on this.  I've attached a couple of pictures and the layout I put together - you'll notice that the preamp section is very similar to what you started with (I really appreciate you starting this post and sharing what you found).  I opted for a standard Princeton style reverb and J12B style tremolo (Thanks to Sluckey for his redrawn J12B layout).  Reverb and Tremolo are good.

I used Tubetown for the relays and they seem to work great.  I did tap into the heater supply and don't seem to have had any issues with noise in the circuit.
I have also added power scaling (whole) amp to attempt to get overdrive at lower levels.  I'm going to change this to the power section only and add a master... full amp just doesn't do it for the tweed channel.
The tweed channel just really doesn't do it.  It doesn't seem to have much bass to start with and the mid-bite doesn't do it either.  I will go through the schematic a few times and I'll put the scope on the amp.
I need to work out if I am losing the tone through the mid-bite section and whether I have made any mistakes.

[philipdfisher]

I meant to say that I'll have a look at your changes you posted (thanks ) and consider doing something similar.  I wan't to work out what may be wrong.  From what you said in your last post it takes a lot of volume to start getting the amp into OD territory.

[Bieworm]

I meant to say that I'll have a look at your changes you posted (thanks ) and consider doing something similar.  I wan't to work out what may be wrong.  From what you said in your last post it takes a lot of volume to start getting the amp into OD territory.

The volume problem was countered with the change of the PI to LPT type.
The OD  was too fizzy and at some point I just gave up on it. Too much frustration and excessive tweaking..altering...
I wired the OD to a setup I was sure I was going to like .
Funny to see my amp layout.. kinda😉😉😉

[philipdfisher]

The LTP would give you a bit more gain compared to the paraphrase… you may even get a bit of PI drive.  Thanks for sharing your preamp section.  I’ll try a couple of tweaks with the current circuit and may go down the same route as you.  The Blackface channel and amp as a whole is brilliant.  I am running on an Alessandro GA-SC64. BTW….first time I have been running on relays too. 

[Bieworm]

The LTP would give you a bit more gain compared to the paraphrase… you may even get a bit of PI drive.  Thanks for sharing your preamp section.  I’ll try a couple of tweaks with the current circuit and may go down the same route as you.  The Blackface channel and amp as a whole is brilliant.  I am running on an Alessandro GA-SC64. BTW….first time I have been running on relays too.

I changed the treble cap to 500p too on the BF channel. And I upped the mid resistor to 27k.. but I'm not a BF guy anyway😉
You're wrong about the LPT geving more gain than the paraphase.  It's the other way around.. I tried to tame the gain/fizz. The LTP tamed that right away.
I also think design wise the last B+ filter cap has too many triodes on it. I will put this amp on the bench some day and add some more filter caps in parallel to sort that out.
I started drawing the schematic to completely separate the preamps and add another triode to go AB763 and 2204.. but I started other projects since then and put those ideas aside fir another time. Maybe that time has come... lol.

[philipdfisher]

Yep, your right on the gain of the paraphrase vs LTP … senior moment for me.  Well spotted on the gain stages per node … ideally 2 per node.  BF channel, I can see you like your mids with the 27k … I may give this a try. I’ll have a look at the current setup and work out what’s not right.  I may go down 6G3 LTP but leave it cathode biased … it would be good to see if I can get a similar setup as the Imperial.  It’s just not quite there

[Bieworm]

Yep, your right on the gain of the paraphrase vs LTP … senior moment for me.  Well spotted on the gain stages per node … ideally 2 per node.  BF channel, I can see you like your mids with the 27k … I may give this a try. I’ll have a look at the current setup and work out what’s not right.  I may go down 6G3 LTP but leave it cathode biased … it would be good to see if I can get a similar setup as the Imperial.  It’s just not quite there

The 500p treble cap was a huuuuge difference too