Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on April 18, 2019, 01:10:46 am
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Hi guys, There has been a fair bit of talk about the Soldano SLO around the local guys and all rave about them.
Not that I NEED a 100w monster.
So in my travels on the net this came up. :worthy1:
http://diy-fever.com/amps/5-watt-slo/
What a beast!!!!
I quickly contacted my valve supplier and he's got hundreds of EL91s, great.
As you can see Gary Moore is at the top of the list of my favourites and I was unaware that he played SLO's. :huh:
This one always makes me CRY :sad2: :sad2:
So a tribute the greatest blues guitarist.
(https://i.imgur.com/fz5vIGZ.jpg)
Because the EL91 are plentiful I'm going up the output to about 10w, if I'm lucky
(https://i.imgur.com/kZn6Nxl.jpg)
The VVR will keep the EL91s happy and the preamp, PI will get the full treatment
The schematics will be updated as we go along.
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wondering if it is even possible to get 10W out of a pair of EL91 without pushing them too hard? maybe 6-7W pushed hard. EL90 (6AQ5) will do 10W or a pair of 6V6 with same B+ and more common 10Ka-a OT will get you your 10W. EL91 want 15K Ra-a to make just under 5W.
--pete
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:think1:
+ 1 for Pete
Franco
EDIT: May be EL95 Is your tube (note it is not a 6aq5 that Is an El90/6aq5 tube)
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Hi guys, I have added another pair of EL91, I got them for free, so why not.
pete,
I have look at a few datasheets and I had the Raa to be around 20k for two valves.
Now that I have added two more valves I was looking for an OT of 10k, I have a vintage OT that is close to 10k but I was going to use it elsewhere.
We have line transformers that work well in these low watt amps and the Raa is around 9K.
Do you think 9k will be OK for four valves?
Thanks
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I think your bias supply is missing a resistor to ground after the classx cap.
Like in the circuit bottom of this page:
http://www.valvewizard.co.uk/bias.html (http://www.valvewizard.co.uk/bias.html)
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Hi guys, I have added another pair of EL91, I got them for free, so why not.
pete,
I have look at a few datasheets and I had the Raa to be around 20k for two valves.
Now that I have added two more valves I was looking for an OT of 10k, I have a vintage OT that is close to 10k but I was going to use it elsewhere.
We have line transformers that work well in these low watt amps and the Raa is around 9K.
Do you think 9k will be OK for four valves?
Thanks
yes.
--pete
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I think your bias supply is missing a resistor to ground after the classx cap.
Like in the circuit bottom of this page:
http://www.valvewizard.co.uk/bias.html (http://www.valvewizard.co.uk/bias.html)
Thanks..
The shems need some tweaking.
Thanks pete. :thumbsup:
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with the VVR the way you have it configured would allow B+ to EL91 to reach over 350V and melt-down would likely result: i added a divider network that sets the B+ window to about 95V - 250V - bear in mind it's sim so it would close for the MOSFET i selected, however, YMMV. reduce R10 to up max B+ output of the VVR.
the bias supply shown has a window of about -15V to -25V - spec sheets say you want -19V @ 250V B+.
--pete
EDIT: VVR with fixed bias can be tricky - ideally, you'd want to track bias V with VVR B+.
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I think you should build this however you want. So, I have no agenda for you.
My preference with higher gain amps is delay over reverb. And if you used a mosfet for the CF, you could save a tube and still have an active FX loop. * see attached schematic
While I really like the "one tube reverb", I think on a higher gain amp like the Soldano that I would probably prefer an active FX loop with delay.
With respect, Tubenit
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I've played around a lot with EL91's for low watt amps. Proper power pentode in a small bottle/small disipation format and better to my ears than pushing small triodes like 12AU7/ECC99. I've used them single ended and push-pull however not fixed bias. My current push-pull low watt amp runs a pair with 265V anode, 10.5V cathode via a shared 390R resistor. I use a Hammond 125C set for 17.6K:8Ohms. More than loud enough for home use so I have VVR on that as well.
I have one in a single ended amp that I've made switchable with an EL90 (different pin-out) - i.e. one 7 pin socket and a switch to select what you put in there. The EL90 is a smaller glass and lower Va max 6V6.
I bought a box full of EL91's on the cheap. Mullard branded but mil spec so dual EL91 and CV136 labelling. They were used by the military as the PA in Eddystone radios.
I'll watch your build with interest!
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TIMBOOOO! Not to rain on the parade, but are you sure Gary is using that amp? I see the SLO and some Fender "thing" but the mic is on the Marshall Bluesbreaker. You know this guy's rig better than me because I guess you are a fan? :l2:
BTW, you are still my BEST friend! :icon_biggrin:
Jim
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with the VVR the way you have it configured would allow B+ to EL91 to reach over 350V and melt-down would likely result: i added a divider network that sets the B+ window to about 95V - 250V - bear in mind it's sim so it would close for the MOSFET i selected, however, YMMV. reduce R10 to up max B+ output of the VVR.
the bias supply shown has a window of about -15V to -25V - spec sheets say you want -19V @ 250V B+.
--pete
Thanks again pete....
The VVR won't be used as a volume control, so once the circuit is loaded the VVR will be fixed.
Tubenit,
The overall circuit will evolve as I go along.
I have only just started laying out the chassis and have put a couple of contingency's in place that can be added too.
I have not bought the components for the reverb (tank/driver) as yet, so a spare socket could be used as the active FX as per the SLO schematic.
I don't know how much the active FX adds the overall sound of the SLO.
(https://i.imgur.com/oCtibRf.jpg)
(https://i.imgur.com/SX7jPxk.jpg)
My starting point will be getting the bias supply and the relay/heater supply working.
Jim, I can not confirm Gary's use of the SLO.
"You know this guy's rig better than me because I guess you are a fan? :l2:"
:l2: :l2: :l2:
I thought he only played Marshalls?????
"BTW, you are still my BEST friend! :icon_biggrin:"
All Aussie's :worthy1: in your presents cause you are "BON" reincarnated.
The Mayor of Brisbane has just announced the commission of a larger that life statue of Jim "AUSSIE" Bob to be erected at the local football ground next to our League legends.
https://suncorpstadium.com.au/About-Us/Stadium-honours/Statues.aspx
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A good day in the shed...
(https://i.imgur.com/qk9PHMo.jpg)
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I don't know how much the active FX adds the overall sound of the SLO.
I would guess that it would not colour the tone much at all? Especially if you set up the FX to be parallel instead of in series.
with respect, Tubenit
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Thanks T, The SLO schematic has an active FX loop, I deleted it as I was not really keen on it, but you have a good point.
Point to point makes it easy to change things on the fly.
So I'll add it in.
I have a Belton brick on the shelf, so I might investigate a SS circuit for it.
:icon_biggrin:
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There are a number of manufacturers that use the CF as a "send" to the FX loop. Some of the Cornford amps do this. * see attached
IF you're trying to recreate the SLO tone and the SLO amp has an FX loop, then it would make sense to consider one, IMO.
Having said that, again ………. I think you "should" build this however you want. :icon_biggrin: :thumbsup:
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Very cool. What are you using for a PT?
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Very cool. What are you using for a PT?
The PT is a 1:1 isolation transformer that has no heater tap.
Some progress...
(https://i.imgur.com/Lg9gy3N.jpg)
For what it worth I have included the active FX loop as per the SLO schematic.
The reverb will remain. I'm haven't decided on a spring reverb or a Belton brick.
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I used to hang out a bit on the SLOClone forums and I seem to remember people thinking the second cathode follower has an effect on the distortion character. There is a section in Merlin Blencowe's tube preamp book about how cathode followers distort that seems to back up that assertion. When people build them without the effect loop they are advised to leave the whole circuit and omit the send/return jacks. Something to consider.
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This thread has got me looking at SLO circuits again.
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This thread has got me looking at SLO circuits again.
Cool!
Hi guys, Wiring is just about done.
(https://i.imgur.com/8OIqHbo.jpg)
(https://i.imgur.com/3tcsXwS.jpg)
Reverb yet to be added.
I'm also toying with adding a small choke to the preamp power supply. Thoughts.....
The relays will be switched via a foot switch only for the moment.
No "bright caps" added, play with that bit later.
(https://i.imgur.com/ha7cgQT.jpg)
(https://i.imgur.com/pBr4sIJ.jpg)
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Timbooooo!
Ooooooo! Cant wait for this to be done! I have a certain collaboration tune that you need to add your expertise to! Nice work!
Jim
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That's a really NICE build! Great job!
Hope we get a sound clip or You Tube somewhere down the line?
With respect, Tubenit
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Hi guys, We have success :wav:
No problems with startup, just a couple questions.
The depth control doesn't do a lot :dontknow::think1:
The original schematic has a 39k resistor in the FB circuit and connected to the 4ohm speaker tap.
I don't have a 4ohm tap only 8, does the resistor need to be halved??
It goes from zero the flat out in in a small rotation of the gain/volume controls. Reduce the volume controls to 500k?
I'll post voltages after I roll some more EL91 to get a closer matched quad. :thumbsup:
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> I don't have a 4ohm tap only 8, does the resistor need to be halved??
In math: increased by 1.414.
In guitar amps: trim to fit.
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Thanks PRR, Tried a few values and for the moment have settled on a 22K resistor.....
Had a mate play it and results were good.
Feeling it has toooo much gain for the little power tubes, I opted for a 12AT7 in V1 ( yet to try a AU7, AY7 and 5751)
I think the lower gain valve has helped but.....
Clean channel is great, quiet(no hum) the crunch is a little noisy and the OD sounds great with a hum that does not sound like ground or Hz, kinda like a gainy hum.
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kinda like a gainy hum.
If it is this, I've found more than once, an AU7 does the trick. The AU has become my pre tube of choice, I can get >70vac outta 2, more than enough to drive KT88s!
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Thanks shooter.
I looking at the "grid stoppers" and "grid leak resistors" on the output valves as a way to tame some of the gain....
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Hi guys, The SLO CLONE is just about done.
(https://i.imgur.com/8K0H7dE.jpg)
(https://i.imgur.com/jEioj3K.jpg)
(https://i.imgur.com/Jo6bOid.jpg)
(https://i.imgur.com/g13Is1I.jpg)
Hunted down a small hum, turned out to be a dodgy pot and a couple of resistors. :cussing:
Working on a 1x10 cab. :thumbsup:
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Hi guys, Got a bit adventurous with the tolex.
(https://i.imgur.com/1LB0rvo.jpg)
(https://i.imgur.com/VX4b2hR.jpg)
(https://i.imgur.com/fsUK9U0.jpg)
The purple snake skin doesn't show up well in the photo's, very happy with the end result.
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Hi guys, My stunt guitarist has put the amp through some awesome pickin.
Mixed results...
With the chassis in it's new box the hum still persists.
Removed V3 the hum becomes very faint.(controls at 0)
Removed phase inverter hum still remains.
When adjusting the bias the hum almost disappears.
Valves replaced and hum is loud and gets louder with volume controls turned up.
Whilst playing slow and cleanish overall sound was great.
Kicking into overdrive also sounded great when strumming and lightly picking but digging in things started mushing together.
At this point I not sure if this was some blocking distorting.
Even with the split plate resistors on the phase inverter and the 10k grid stoppers I think the grids are still getting a hammering.
My next thought is to add a PPIMV to help tame the drive????
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Hi guys, some more testing has been done...
Haven't been able to track down the hum....
I added a PPIMV and lowering the gain to the EL91s gave better control over the gain/volume pots.
I replaced the pot with resistors and was able to dial in some great drive.
But there is still a little too much drive when the lower notes are played.(notes get a bit flabby)
So my next job will be to replace the .047 coupling caps to the power valves with either .022 or .01
Hopefully this will help the flab.....
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Try 47k grid stoppers on the output tube grids too
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Try 47k grid stoppers on the output tube grids too
Can do!
These oddball valves are a bit of a challange
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Hi guys, Another round of testing and we're getting close.
The .022 coupling caps to the power valves helped with some of the bass overload.
So the 12AX7s were put back into the PI and V1 with better results as a bit of the SLO shimmer was lacking.
Also some of the bottom end was missing. :think1:
Might try some .033s
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Just curious if you're able to try a variety of speakers with the changes when you make them.
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Guys, this one is just about done.
(https://i.imgur.com/MhQIx3V.jpg)
(https://i.imgur.com/FxK6S5Z.jpg)
(https://i.imgur.com/MpVYMlX.jpg)
Hopefully I'll get a clip soon.
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Hi guys, Some nice sound clips....
https://soundcloud.com/user-787861330/sample-1?in=user-787861330/sets/warlock-gto
https://soundcloud.com/user-787861330/sample-2?in=user-787861330/sets/warlock-gto
https://soundcloud.com/user-787861330/sample-3?in=user-787861330/sets/warlock-gto
https://soundcloud.com/user-787861330/sample-4?in=user-787861330/sets/warlock-gto
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sounds awesome
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Timbooo! Sounds awesome! NOW.... I wanna hear you add some scorching Angus lead to the collaboration clip I posted! I just cant imagine a true Brisvegasan would back down from a challenge like that - Eh? :icon_biggrin:
I am concerned, however. It appears that you have a lot of parts left over. Are you sure you are done?
Yer best pal!
Jim
https://i.imgur.com/pBr4sIJ.jpg
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Hi guys, Trying to sort out a bit of a problem.
Seems to be some signal bleeding through somewhere.
When I have the OD channel on and with the OD gain pot at 0 I can turn the OD volume up and get signal passing and it's quite loud.
When I have the crunch channel on and with the normal gain pot at 0 I can turn the normal volume up and get signal passing but only when the volume is near max.
Using a gator lead I can ground out the signal at the .022 on V1b as you would expect.
I'm wondering if the relays will leak signal across the contacts.
https://www.cypax.dk/pdf/FRM1.pdf
I used my scope and got signal at the .022 off v1b. There was also signal on all poles of RLY2.
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There was also signal on all poles of RLY2.
anything on RLY1 since they are in || for power?
I would suspect "sneaking by" over wires before across contacts, but contacts could be sooooo close that a large signal might :dontknow:
I'd temp in a PS just for the relays, maybe temp in a switch in place of contacts, or just swap relays n see
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Great project! :thumbsup:
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.... contacts could be sooooo close that a large signal might
I've read something like that on a Merlin's book
if the contacts are close they can act as a capacitor and AC signal can pass
Franco
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Timbooo!
Your Bright/Normal “paddle handle switch” :icon_biggrin: seems vulnerable as it looks like it extends out past the cab and knobs. You may want to replace it with a smaller ball end switch that’s hunkered down a bit more. Heck just run down to Dick Smith and grab something....
Jim :angel
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Hey Jimbo, Good to see you brushing up on our local icons.
Unfortunately Dick is not in the business any more, sold out to a bigger company for lots of dollars and they drove it into the ground.
Every day you are getting close to being a "Trueblue" Aussie.
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Hi guys, I have confirmed the relays are letting signal through.
Possible need to find relays that will work
OR add another relay that will ground out the channel not used :sad2:
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Ciao TIMBO
You have a PM
Franco
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In the original SLO100, the normal channel is not disconnected when the OD is engaged. Both channels are mixed together before the final gain stage before fx send.
Normally, the OD will dominate the normal channel, but if you set OD gain very low, bleed through seems likely.
Since it’s tubes and high amplitudes, some capacitive coupling between channels can happen. Muting and/or disconnecting the unused channel is a good idea.
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Cool build ! Looks very nice!
Good idea with lower power output, it'd be nice to hear a high gain preamp with output tube distortion going on, without hitting the Richter scale.
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Do you find any issues with low end? The hammond OPT - primary inductance 5.6H seams very low for the Ra-a of EL91 in push pull?
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Do you find any issues with low end? The hammond OPT - primary inductance 5.6H seams very low for the Ra-a of EL91 in push pull?
Hey mate, I'm actually using a 100v line transformer as my OT.
The specs are 30Hz-20KHz +-3dB.
Seems to work well.
In the original SLO100, the normal channel is not disconnected when the OD is engaged. Both channels are mixed together before the final gain stage before fx send.
Normally, the OD will dominate the normal channel, but if you set OD gain very low, bleed through seems likely.
Since it’s tubes and high amplitudes, some capacitive coupling between channels can happen. Muting and/or disconnecting the unused channel is a good idea.
With a bit research this seems to be a part of the amps MOJO :dontknow:
So I'll do some rewiring and see what I get.
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Great looking build ! Sound clips are nice, too !
But I just have to chime in here about the SLO circuit. So beware, opinions are about fly !
Caveat: I have not played through, or even heard a genuine SLO in person.
I have, however, OWNED a mesa rectifier, which is VERY similar to the SLO hi gain channel.
And, I have built several SLO/rectifier circuits.
And, TO ME, the rectifier/SLO sound is a mess.
BUT, I've found through building the circuit, and schematic research, it can be made better.
The flab low end you mentioned, I agree. Yuck. Try, if you have the time/inspiration, changing the coupling caps to something like 0.004uF. In your circuit, that would be the 0.02uF caps you have at V1 pin6, V2 pin6, and V2 pin1.
Also, the 1M to ground at V2 pin 2 can be lowered to about 100K. The channel will lose a lot of noise, and gain tons of clarity.
Check out some of Bogners high gain schematics, and have a look at the Vai carvin legacy schematic.
I'm not judging your build, the sound clips I listened to on my phone, they sound fine, considering I'm hearing them on a Samsung Galaxy :-)