SLOW DRIVE 84

[TIMBO]

Hi guys, Tubenits LOW WATT PP really caught my eye and got me thinking.  I have built some great amps but they all have one thing in common, their TOO LOUD for bedroom level even with VVR's and PPIMV's but i wouldn't have them any other way. The other reason they caught my eye is that i have two 125d OTs for jonks and no home for them till now and a quick look at a local tube supplier got me matched ECL84's (one pair Phillips and one pair Telefunken ) for $20 a pair.  I liked the tone of the TOS so i'm hoping that SLOW DRIVE 84 clean, sounds as good. The PT was also acquired locally at a good price so it is looking to be a fairly cheep amp   
At this stage it has no OD section and the PT has no Heater tap and so another tranny is needed and the Data on the valves says that i need about just under 2A if i have read then correctly and a bigger tranny to cover more tube heaters was starting to cost a pretty penny so what is one to do 
Awhile back when looking over some tasty guitars and gear at a local music shop i happened onto an interesting amp called The Tubescreamer amp by Ibanez and was on the net in a flash to get the info and it is as said an amp with a built in TS 808, what a great idea.

  The SLOW DRIVE 84 is created 
The transformer secondary after rect could be about 325v which will be a tad high for the ECL84s will this be a problem can i just put a resistor in instead of the choke to knock down the volts a bit (any idea what size??)
The voltage regulators are only rated at 1A which is fine for the SS stuff but for the heaters i am unable to find any regulators that are rated higher than 1A although i can run the SS off the 9v tap which will give me just over 12v to the regulator and don't need any more that 1A.
The heaters can be run off the 6v tap and supplied with AC or can the 9v rectified have a resistor in place of the regulator to bring down the volts a bit. Thanks

[tubenit]

I am not smart enough to know if the 323v will be too much for the plates or not?  It might work?  If your chassis has room, perhaps you could use a 5v transformer and use a GZ34?  OR you could use a VVR to keep the plate voltages lower while allowing enough voltage on the preamp.

As much as I liked the tone of the 6BM8, I do like the tone of the ECL84 even more.  The ECL84 has incredible bass response to it, IMO.  I'm stunned that such a small tube has such good bass response.

The SoLow Watt is around 3-4 watts I guess?  While that still gets a decent volume, it does make a great bedroom volume type amp with very nice harmonics and sustain.  I really enjoy mine. IF you're wanting a great amp for sustain at much lower volumes than the TOS, this is a good amp to consider.

I would recommend not having the typical Marshallish master volume and use the PPIMV instead which is what I have now. Initially I had a master volume & a PPIMV.

I completely removed the Marshallish MV because with everything dimed, I was getting some slight oscillation.  With the MV removed, I can dime everything with NO issues at all. Not even a hint of oscillation.  Could of been a layout issue though since my chassis is quite small and everything is very cramped.  Maybe there will be no issue for you at all?  

My impression is the PPIMV may be  needed with the ECL84 pentodes?  This is more of a gut level impression than anything else. With my PPIMV, it is usually dialed between 5-8 & it is used more than the volume knob to actually adjust volume.  Please note that I have 200k resistors across the 220k dual gang pots. That is effectively giving around 100k to ground  for the grid resistor. Still has plenty of volume and overdrive for me.

The .01 off the 5879 plate may or may not be your best choice. If you don't like it & the amp is too bass oriented, then try the .0047 or a .0068.

I can get almost any note to sustain all the way to feedback so the amp really does have some singing sustain to it.  

Having said that, adding the TS808 is still a very interesting idea and I think would add even more versatility to the amp. You could dial the volume knob to "3" & kick in the TS808 and have a whole 'nother tone.

VERY cool idea and design!!!  Really looking to hear how this turns out. I think you'll have a great amp.

With respect, Tubenit

[sluckey]

The voltage regulators are only rated at 1A which is fine for the SS stuff but for the heaters i am unable to find any regulators that are rated higher than 1A

The LM123K in a TO-3 package is rated for 3 amps. The simple circuit below will allow you to adjust it's output from 5 to about 12 volts.

although i can run the SS off the 9v tap which will give me just over 12v to the regulator and don't need any more that 1A.

Applying 12v peak pulsating dc to a 12 volt regulator will not work very well. The regulator output will be lower than expected and will have a lot of 120Hz switching noise. You need a higher input to provide more headroom for the regulator to work properly.

The heaters can be run off the 6v tap and supplied with AC or can the 9v rectified have a resistor in place of the regulator to bring down the volts a bit.

The heaters are a constant load. Why would you want to regulate them? Just use a dropping resistor and filter the dc very well.

[kagliostro]

I think that for only the SS circuit 1A regulator is fine

as at Mouser the LM123K is indicated as not disposable because obsolete

you can use a 5A TO220 LM338T (~€ 2.02 - at Mouser)
(a 5A TO3 LM338K will be very expensive ~€ 8.38 till € 49.95 - at Mouser)

about filaments you can go also with the 6v and you are fine

or if you want an exact 6.3v use an LM338T (with heatsink) on the 9v winding and set it for 6.3v

5879 (6.3v) accepts heater voltage within +- 10%

12AX7 (6.3v) accepts heater voltage within +- 20%

ECL84 (6.3v) not find data but the 6DX8 equivalent tube accepts heater voltage within +- 0.6v

the ECL84 is rated for Va 250V - Va at cutoff 550V

in Tubenit's schematic there are 252v on ECL84 plates, so I think it will be better to lower B+  from the 325v you have

you can try with two big resistor between the transformer and the SS bridge

I think a pair of 7W resistors say 100R / 150R is something to try

or, if you prefer, there are other more sophisticated solutions

Kagliostro

[tubenit]

in Tubenit's schematic there are 252v on ECL84 plates, so I think it will be better to lower B+ a from the 325v you have

I ended up with 252v because the 190-190 PT would only produce that with the solid state rectifier.  It wasn't intentional. To be honest, I would have liked to have been able to experiment with somewhat higher voltage on the preamp. Don't know if it would've sounded "better or worse", but I would've like to have had the chance to try it both ways?

In your situation, I might be inclined to try to drop the voltage to the ECL84 plates to 300v (max rated voltage) if possible?

With respect, Tubenit

[DummyLoad]

The voltage regulators are only rated at 1A which is fine for the SS stuff but for the heaters i am unable to find any regulators that are rated higher than 1A

LT-1083, LT1084, LT1085 - 7.5A, 5A, and 3A respectively. LT-1086 is 1.5A - all are still in production.

http://www.linear.com/product/LT1083

the only thing i like to use  linear VR for is filaments of very high gain amps. works very well. ditch the pot and stick a 1N400x diode under the GND pin of a 5V regulator and you'll be @ ~6.0-6.2VDC Vout. 

--DL

[DummyLoad]

oh yeah, the name of your amp... this song popped into thoughts... 

 

Slow Ride- Foghat (Full Version)

[TIMBO]

Nice one DL    An all time favourite and it did tweak a memory.Thanks

The schem for the SS stuff has the working voltage between 9 and 12v and looking at the tranny again it has a 12v tap but at first i was thinking that the 12vs after rect  may have been a bit high for the 12v regulator. I know that these FX circuits usually run on 9v but i'm sure i read that they do work better at a higher voltage, ideas????
As for the heaters i might do some test runs with AC and DC. Thanks

[DummyLoad]

12vs after rect  may have been a bit high for the 12v regulator.


in this case we with the LT-108x stuff we don't care. specs say you can have up to 30V input differential to output V.

bear in mind though that the regulator dissipates power based on Vin-Vout/Iout. to clarify, if you have a 5V regulator w/ 20VDC Vin and the load is 1 Amp @ 5V out, then the regulator will be dissipating 15 Watts. You'll need a *large* heat-sink in that scenario.

--DL

[kagliostro]

12v AC is plenty fine

use a regulator (with heatsink) and go for 6.3v output

there are many cheap regulator you can use

a 3A LD1085 (€ 1.91 at Mouser) is one

and

the LM317 is rated for an input of 40v, so no problems also for this

here a schematic for dual regulator (1 for SS, the other for filament)

only you must choice the right IC as to have the current you need

instead of LM7805 you can use an LM7809 (1A) for SS circuit

and an LM338T (5A) for the filament circuit

or, as the price is not very high, use both LM338T and adapt the schematic to it

the schematic show the use of a CT 15v-0-15v transformer and full wave rectify with two diodes

but you can use a single winding Transformer and a bridge

Kagliostro

[kagliostro]

Based on the previous schematic and on LM338T & LM7805

This is my first eagle job (not started from scratch)

I added two 1N4148 between the central terminal of the LM7805 and ground as to have ~6.3v for filaments

on the board there are three jumper one is for continuity of the circuit

the other two

one under the LM338T the other between the LM338T and the LM7805
(this two must be used only one at a time)

with one you have the + voltage coming from rectifier to both the input of the regulators

with the other the output of the LM338T go to the input of the LN7805

the idea is to have a 12.6v and 6.3v from the same heater supply in the case there are tubes with only 12.6v and only 6.3v (without possibilities to connect heater in other way)

Revise the board with the schematic, as I told is my absolute first Eagle job

my intention is to use this or a similar power supply for three tube preamps I'm going to build

Kagliostro

[TIMBO]

Thanks Franco, all good info 

[kagliostro]

I've learned how to export a PCB as to be printed without Eagle

open the attached file with paint and print it

or alternatively paste the image in word

in both case it will be print of the correct size

Kagliostro

[TIMBO]

Hi guys, I need to lower the B+ by about 25v and when reading through the other post came across this posted by Willabe (6G15 stand alone schem) and think it will be just what i'm looking for. So hopefully Willabe will chime in with any comments on its performance and how the small value caps related to the circuit and what the voltage drop was at "A" Thanks



http://www.el34world.com/Forum/index.php?topic=13082.msg122183#msg122183

[Willabe]

Hi Timbo,

On the verb unit the voltage only dropped a volt or 2 at each of the B+ supply line points, A,B and C. The PT secondary HT cross line cap should be raited for DCv.

The small value caps are to get rid of ss diode hash/noise. I also used ultra fast diodes to lessen the ss diode hash.

I got this from KOC's TUT books. All the parts, R's, C's and uf diodes work together to clean up the ss diode hash. The 3, 10R 5w R's also help limit B+ current inrush.

The verb turned out very quite and works/sounds very good to me.



              Brad      

[Willabe]

Merlin has much of the same info in his book and on line.


       Brad     

[TIMBO]

Thanks Brad, I might try some R's slightly bigger than the 10R's and see if this will work.

[Willabe]

You already know this, but the bigger the R in series with the B+ line the more sag you get. Can be a problem.

Power Scaling, VVR is nice for the $$, ease of hook up and small space. You can set it and forget it inside, you don't have to have a pot with access on the panel.


      Brad        

[TIMBO]

Hi guys, It's been a productive day even though its been pouring rain all day ( had to stay home and build amps  )
Picked up the chassis from metal shop and realised i made it too wide but thats OK this gives me a bit more room on the inside to maybe put the heater transformer and OT??
The heater tanny also will power the SS stuff so keeping it in the left corner should cause no problems  
The OT position also i hope is not going to cause problems.

Is this good/bad idea. Thanks

The knobs are the position of the tubes just haven't cut the holes yet. 

[kagliostro]

Hi Timbo

As I can see you used hybrid Turret PCB Board for this build

only curious about the method you use for PCB

I use laser printer on usual or photo paper than transfer the image with an iron

and you ?

Kagliostro

[Willabe]

Given a choice, I'd would rather have any iron on the outside of the chassis for free air flow and less noise. Why introduce a heat source even a small one and a stray magnetic field inside the chassis? As long as the chassis is going into some kind of cab. to protect them I'd keep them on the outside if I could. I don't see this as a good thing to do.


                        Brad      

[TIMBO]

Hi Guy's, Fired up the SLOW DRIVE and no problems so far  Took some voltages and as expected they are a little high.

NODES as follows :-

After rect - 348v
NODE A - 338v
NODE B - 309v
NODE C - 274v
NODE D - 257v

ECL84 :-
PIN 2 - 176v
PIN 6 - 337v
PIN 9 - 306v

Across 1ohm resistor - 19.6mA
Heaters - 2.8v/leg
I have not tried the guitar as yet as i would like some input on whether i need to lower the pin voltages before i proceed. Thanks

[TIMBO]

Hi guy's, My voltages are about 80v too high @ node "A" and i think the only way to bring it down is with a VVR .I have not use a VVR to reduce the volts for the whole amp but i think this would be an easy insert as shown in the schem.Any problems doing it this way?? Thanks

[sluckey]

Before you do the VVR try just disconnecting the 47µF cap that's connected to the bridge. This will convert to a choke input filter which will give less B+ if the choke is big enough. Easy to try.

Have you run a guitar through the amp yet?

[tubenit]

Follow Sluckey's advice first prior to trying a VVR.  Sluckey has given me tons of great advice that resolved amp building problems for me.

However, IF that doesn't resolve your issue,  I would do the VVR this way and NOT VVR the entire amp.

With respect, Tubenit

[tubenit]

Follow Sluckey's advice first prior to trying a VVR.  Sluckey has given me tons of great advice that resolved amp building problems for me.

However, IF that doesn't resolve your issue,  I would do the VVR this way and NOT VVR the entire amp.

EDIT:  sorry, I should have indicated the 4.7k to be 6.8k or even 8.2k.  It needs to be increased to compensate.

With respect, Tubenit

[TIMBO]

Hi guy's, Poked and prodded a bit with some good results. I did not try Sluckeys idea as it is too hard to remove the Cap as it is soldered on the under side of the board. I plugged the guitar in and sounded good but with a lot of background hiss/white noise at higher volume. At the moment i have 330v between plate and cathode and 18.6mA across the one ohm resistor (5.8v across cathode resistor) giving me about 5W per tube. So any ideas before i insert the VVR. Thanks

[TIMBO]

HI Guys,Got the VVR up and running now i can get the right voltages on the ECL84s although it did not sound bad when it had 330v on the plates. I was hoping that dropping the voltage may help with the static/white noise i was getting at the higher volume but i think its the SS stuff giving me grief. I also has the HT fuse pop on me a few times, so its going to be a fun time to track down the problem. Any thoughts, Thanks

[TIMBO]

Hi guys, I'm trying a few things to track down the snow/white noise i'm getting. This happens even when no guitar is plugged in but only realy kicks in when the volume is increased to almost max, this is when the volume pot is engaged. When volume pot is disengaged it still has the white noise and a fast buzz as well. I tried moving the ground points around but it remained the same. I disconnected the SS stuff and it did not change. It was there before i added the VVR so i'm sure its not that. With the VVR i was able to get a good match Tubenits voltages as per his schem. I was thinking that the higher voltages may have been the cause of the noise  The other thing that was happening was the HT fuse kept blowing but not the main fuse  I have not come across this problem before so i'm not sure what to do  . The fuse i have is 250v (i'm assuming thats 250v AC ) @500mA then tried 630mA,no good and at the moment i have a 2A fuse thats holding OK. It was asked what size fuse should be on the B+ and it was said to be 500mA . Could the voltage be the cause of the fuse to blow not from the current but maybe the 340v that pumping through it before it hits the VVR.

This is another great little amp that has heaps of balls and can go from very clean to having a HUGE pair and and quite loud for aprox. 8-10W 

Again fighting the BUZZ. Thanks

[tubenit]

I am following your thread with interest.  I don't know what to say about the white noise or buzz?  My amp is pretty quiet at idle.  With everything up to "10", there is some reasonable white noise but less then I'd expect from a higher gain amp. Certainly below what I would expect to be normal limits.  In other words, significantly less white noise than the original Fender Princeton Reverb I owned.

I sure hope you can find the cause! The fact that the fuse has blown has got to be something of a clue.

As I am understanding it, with the tube screamer disengaged, it still does this?  However, I am wondering if you disengaged the tube screamer from the power supply .............. OR the power supply from the PT?

With respect, Tubenit

[TIMBO]

Hi guy's, Ive poked and prodded this thing to death and are unable to find the source of the white noise/ oscillation at higher volume.Its in the amp itself as i tried an input directly into V1 and the noise is still the same but if this was considered to be a HIGH GAIN amp i would say that it might be acceptable. To me it sounds as thought it is passing too much signal and it gets all out of shape when it hits the power tubes. I tried different tubes (ax7,at7,au7) in V2 and they all produce the same result, so could it be the 5879 adding too much gain. I found that on this build ( and similar to the TOS OD drive ) that the volume pot on the 5879 acts more like a gain pot rather than a volume. This is why i have three settings (clean, dirty and overdrive)cause with out the volume pot engaged i was unable to get a real clean, clean. The DIRTY channel ( with volume pot disengaged ) is fantastic and love it as is.

I don't feel that it is the VVR as it remains the same the at any voltage level.I tried different arrangements with the choke and resistor around the "A", "B" nodes and none these made any difference to the noise or even the sound.

I was wondering whether to add some NF to see if the will stabilize the problem and if i did what sort of resistor value would i be looking at maybe something like the 56T 

The noise is more noticeable in the Dirty channel at "5" but kicks in about "8" or "9" in the Clean channel so by engaging the volume pot it seems to reduce this noise a lot. I'm not tech enough to know whether this noise/oscillation will cause any damage to the tubes as the volume that is a good level for me i can live with a little hash  Thanks

   

[tubenit]

Maybe try a paralleled 12AX7 instead of the 5879 in V1?   That again would allow gain options using different 12A_7 tubes.

With respect, Tubenit

[TIMBO]

Hi guys, The SLOW DRIVE 84 is a no goer  I am unable to get a happy medium with the setup as is. The amp itself has a great sound and i think the ECL84s has heaps of punch for a little tube. I can't find the reason for the oscillation/squeal at higher volume and the white noise that is present at various levels (even with no guitar plugged in). I'm sure that the problem is somewhere in the layout around the ECL84s. Tubenit i tried the paralleled 12A_7 but this did not improve on the problem.

The SS overdrive circuit was a GM ARTS Overdrive Pedal that has an OK sound but when it was engaged this made the noises worse and to be able to really get the overdrive to kickin meant turning the amp gain pot down to about "2" any higher the whole thing got out of shape.The buffer was also a problem that caused some grief.

I do not have enough knowledge or equipment to be able find the sources of the problems and when they arise and i have to rely on you guys to help and when that fails i have no other options but to put on the shelf with other " WOULD HAVE BEEN GOOD IF IT HAD'A WORKED"  So hopefully in the future when i gain more knowledge i might dust her off and try again. Thanks to all 

[tubenit]

If a paralleled 12A_7 didn't resolve it, then I think it's some other issue besides just too much gain.

Sorry to hear it didn't work out. I am wondering if it was a layout problem somehow?  My SoLow Watt doesn't have the oscillation at all & I can dime all the controls.  I wonder if taking a paralleled terminal approach & using Hoffman's ground scheme would resolve the issue.

With respect, Tubenit