BOOGIE TO BLUES

[TIMBO]

Hi guys, I have a transformer set that was taken from a National (made in Japan I think) PA type amp.
And I didn't get ALL the info I needed before removing them from the chassis.
Good size transformers

PT measures about 4" square and 1.5" deep


The original info I have is it had a pair of EL34s in it.
So, I thinking that the power supply could look like this.

[tubenit]

The PT says 65ma ?    Is that correct?   And if so,  can that support EL34's?

With respect, Tubenit

[sluckey]

I think your proposed circuit will be fine. One thing though... That 42V is a separate winding. It's not a tap on the HT winging. Two terminals involved, so connect one to ground and the other to the bias circuit.

[chocopower]

I think the 65mA sec. is for EL34 screens and preamp tubes.
Plates use the other H.V. sec.

[2deaf]

The standby switch only switches between half-wave and full-wave rectification.  I wouldn't want HT on the screens if a standby cut the HT on the plates, so I like the idea of a screen type standby.  Maybe put the switch on the right side of the coil and a diode on the left side of the 10K/3W resistor with a 1M resistor to ground on the right side? 

[kagliostro]

God bless those who write specifications on transformers

Franco

[sluckey]

God bless those who write specifications on transformers

Franco

Ain't that nice!

[TIMBO]

Thanks guys,With a full wave bridge the voltage on the power valves plates should be around 560v.
Does this sound ok for a pair of EL34s????

So thoughts are to convert the SS bridge to HYBRID http://www.valvewizard.co.uk/bridge.html and also to add some SAG.

Now some other thoughts...
The original amp used a 6BL8 phase inverter and got it's heater supply from the 6.3v @ .6mAs.
And the two EL34s and three 12AX7 preamp from the 6.3v @ 4A.
This fits neat for five preamp and two EL34s (new build)
But the OT has a 6k primary, that I would think doesn't suit a pair of EL34 but would work for a pair of 6L6GC.
Using 6L6gc would also be a bit easier on the heater supply.


Here is where I'm going with this...
I'm recycling some parts from a build of many moons ago.
I think what kicked off this again is a guy liked an amp build I did that had great bottom end.
Mesa Boogie Dual Rectifier is seen as the king of CHUNK CHUNK heavy metal.
So can the BOOGIE be used for BLUES.
Found this

The schematic is the Dual rectifier Solo head.


Two channels ORANGE and RED
With switching to change the modes.
Orange - clean,normal and modern
RED - normal and vintage

This cheat sheet shows the switching used to create the effects

[tubenit]

I will be watching this thread with interest!  You consistently come up with some great build ideas!

With repect, Tubenit

[sluckey]

That OT would reflect 3K to the plates if you put a 4Ω speaker load on the 8Ω tap. I would not want to use 6L6 with this high B+. If the amp originally had EL34s there's no reason to not use EL34s with that iron.

[chocopower]

With 560v on plates, a 6k load seams logical, isn't?

[PRR]

> With 560v on plates, a 6k load seams logical, isn't?

Agree. The tubes do not have strong preference. The voltage and safe power suggest the happy load. Raise voltage 10%, load should go up 21%. I'd think 6k6 even 8K for two large tubes at 560V.

[TIMBO]

Thanks guys.
Tweaked the power supply a bit.


The boogie schematic had a mistake and Valve Wizard confirmed that having two sets of artificial CT's on both sides of the bridge rectifier was wrong.
So using the 6.3v .6A heater supply I thought it a good idea to supply V1 and V2 with DC.
It was mention, care was needed with the amount current that the transformer could supply as DC would likely to draw twice as much.
So a 6.3v 500mA transformer was connected and left for a good 10 minutes and the transformer was not even warm, so I should think the .6A will be fine.
http://www.valvewizard.co.uk/heater.html

I really like the idea of the rectifier valve for the EL34 plates.
An extra transformer will be needed.
Thoughts......

[TIMBO]

Hi guys, A little progress.

These two circuit boards have the tone stacks, gain, presence, master volumes for the two colour channels.

This 6 pole 2way rotary switch will switch between the RED and ORANGE channels
It will operate :-
SW 1&2
SW 5&6
SW 8&9
SW 14&15
So for the moment switching between colour channels will be done manually.

To save a bit of space the preamp, reverb and PI filter caps are mounted on the back of the chassis.

This small board will rectify a 6.3v @.6A tap to supply DC to V1 and V2 heaters

[TIMBO]

Hi guys, A bit of a head scratcher.






A bit more going over the circuit to do.
Fire up and get the basics working.

Then I'll add some temporary switches to see how they effect the sound/tone.

[DummyLoad]

very nice tim!


--pete

[TIMBO]

Thanks pete, I'll fire it up over the next few days.

http://www.freeinfosociety.com/electronics/schemview.php?id=507

This is the schematic I'm working off.

As I said I will add some temporary switch and then delete the ones that voice the "BOOGIE" in the circuit.

I'm hoping that I can also replace some cap values to tame some of the boogie beast.

[TIMBO]

Hi guys, Fired up kinda OK, no smoke.
Getting the bias right been a bit of a job.

At the moment I have
Plates - 615v
Screens - 410v
Cathodes (across 1ohm) - 26mAs

The PT has 230v and 240v primary taps, currently connected to the 240v tap with wall voltage approx. 245v
Will connecting to the 230v decrease the secondary output, or are the 6CA7s happy at that voltage??

[PRR]

> 230v and 240v primary taps, currently connected to the 240v tap with wall voltage approx. 245v
Will connecting to the 230v decrease the secondary output

No. Probably a real bad idea. You will get 640V DC and probably a hot PT.

[TIMBO]

Thanks PRR.
Injected life and the BOOGIE lives.



Voltages look.
PI and preamp voltage are a touch lower than the marked voltages on the original boogie schematic.

Wall voltage is high, would normally be around 247v, so this is pushing up the secondary voltage of 435v to 460v.

So if I have my math correct plate dissipation is 22w

Would really like to reduce the plate voltage on the 6CA7, could another R/C be added??

[PRR]

> Would really like to reduce the plate voltage on the 6CA7

6CA7/EL34 is an 800V tube. Why?

You are mid-way between two conditions suggested by Philips.

[TIMBO]

Thanks PRR, Yeah not really up to speed with how all that works.

I have a pair of OLD 6CA7 in, they both tested 100%, so if they happy at my settings I'll leave it be.

Just have to say, this thing is LOUD!!!!!

Added a PPIMV.

[Ritchie200]

Timbo

Too cool!  Sound clips?

Jim

[TIMBO]

Thanks mate.

A little way off a sound clip yet.

[TIMBO]

Hi guys, Concentrating of the ORANGE channel.

I have tweaked a few values to get a cleaner sound.
But the way the valves are setup it's not gonna be real clean.

Switching is as follows
SW3a - off
SW3b - off
SW4 - off
SW10 - off
SW16 - off
SW19 - on
SW20 - on
With these settings and changing the TS values possible the best I going to get it.
Unless there is something I have overlooked with out changing the main circuit.

I'm getting a small amount of signal bleed through, when the gain is turned down and the master is turned up, faint sounds can be heard at the speaker??

[TIMBO]

Hi guys, The Boogie been put on hold till the test pilot is available.

This will give me a better idea of what sounds can be achieved via the different switching.
Then I can nut out some sort switching arrangement.

Thanks