I tend to use star grounding to reduce ground noise.
Not much ground noise on input due to low currents but the output valves can generate a bit of noise in the ground.
I used DC heater supply once to get rid of hum and it made no difference as noise was coming from elsewhere.
I have used AC heater supply since and never had any problems.
50Hz sine wave doesn't radiate a lot.
Not much ground noise on input due to low currents but the output valves can generate a bit of noise in the ground.
I used DC heater supply once to get rid of hum and it made no difference as noise was coming from elsewhere.
I have used AC heater supply since and never had any problems.
50Hz sine wave doesn't radiate a lot.
A fairly standard CC>CF.
This can be done with many tubes, Bottlehead pre uses 12A-something-7, i have one with 6H23∏ (6922), there is a long thread using the 6SN7.
Can be fairly easily direct coupled really benefits from CSS at the top of the first stage, and th ebottom of the second stage.
I’m late to the party, the link in post #1 has turned to spam, i wonder if it is the same topology?
dave
That is absolutely correct. I heard about this tube years ago and started to read up on old tubes, this one is special. At least the web is full of people that speaks highly about this tube.
The Philips E88CC SQ is a tube that beats every other preamp tube there is. It lasts longer, has zero microphonics, its gold plated pins is for a reason.
Gold is bling, no doubt, but them pins are gold plated for a reason.
Gold don't corrode, loose connections will hold longer than other metals since gold makes good molecular binding even in a loose connection.
Audiophiles love this tube because it is amazing as an A.F. amp. ..funny thing is that it was never meant to work with audio frequencies at all.
Oh, and the price ..USD $250 each from 'the tube store'... check it out:
https://www.thetubestore.com/philips-sq-e88cc-6922
I have 4 Philips NOS E88CC SQ in my collection.. 20 years ago, my boss told me to clean out the old electronic repair shop and throw all the tubes in the garbage. I did not. Got a box with 300+ Philips tubes and 30+ from other producers around the world. Was 5 E88CC's in the box but one had cracked glass and was destroyed. All white on top.
A lot of the Philips tubes was P-series that don't use 6.3 volt on filament, but higher voltage. Built a Marshall jcm800 preamp (I copied the original circuit) with ecc83 and a single ended output with a Philips NOS PL84. Those need 15 volt on filament and was meant to be working as A.F. in Philips TV's.
OK, writing this comment is maybe a waste, you probably know all this already.
But others may not, and maybe find my supplement to what you wrote useful.
Old tubes can break your heart. The one on the right in the photo has gone gassy. Getter flashing has turned white. Some old tubes just go supernova and draw a lot of current, even if they don't go gassy. Shorts perhaps?
There's no guarantee an old tube will have low microphonics. I sold off a bunch of my USA Amperex 6922 tubes. I did tell the buyers they weren't suitable for phono stage use. They also sounded harsh to me.
If you want to experiment on a budget, get some NOS Tesla (not JJ) ECC88s. There seems to be lots still around. They kind of have the Mullard Blackburn rockem', sockem' vibe, for a whole lot less money and in my experience, tend to be non-microphonic. If you fancy the Philips Heerlen soft-ish sound try some JJ E88CC.
Steve
There's no guarantee an old tube will have low microphonics. I sold off a bunch of my USA Amperex 6922 tubes. I did tell the buyers they weren't suitable for phono stage use. They also sounded harsh to me.
If you want to experiment on a budget, get some NOS Tesla (not JJ) ECC88s. There seems to be lots still around. They kind of have the Mullard Blackburn rockem', sockem' vibe, for a whole lot less money and in my experience, tend to be non-microphonic. If you fancy the Philips Heerlen soft-ish sound try some JJ E88CC.
Steve
Yea, you are right about that. When I got these tubes I did not know much about the technology.
All the E88CC tubes are brand new, they have never been in a socket after they left the testbench at Philips. I have no need to start experimenting with them. The one that have drawn gasses have a visible crack in the glass that cant be seen in that picture, but it came out of the box like that.
I red-plated a NOS Telefunken EL84 when I was trying to build my first amplifier. Experimenting with those things are not the smartest thing when you are an amateur that is learning... I guess I learned something from it, but it was a heavy loss to bear..
Being a educated and certified electrician did not help. In school we learned about transistors, and the old tube technology got mentioned for 3 seconds. Tubes was seen as "useless obsolete technology" the second the transistor was a reality.
So when I had a bunch of tubes..i did not know much about them. So I started to read up about them.
That was 20 yrs ago. Them tubes got me into guitar playing, and audio, tube audio in general. Why do guitarists prefer tubes?
They sound amazing. Compared to any transistor amp.. For a guitarist the way tubes clip and distort the guitar sound is just magic, and I guess you have to experience it to fully understand it.
I made a stereo hifi amp using EL34 output, 12ax7 preamp, & 12au7 as phase inverters driving the el34. It looks like its going to burn down your house, but it it has been a good boy for 6 yrs now and is in use every day. I started the build as a cathode biased PP delivering 15 watts/channel, and learned more and more as the build went on. Coiled all the transformers myself and used calculating software (OTP Design Assistant) made by Yves Monmagnon to get a good design simulated. That software is freeware on the web, and it is very good!
I recycled transformers and copper wire, but pretty much everything inside is high quality new components. The circuit is of course stolen from someone but its ok to know that it will work if the build is done properly.
The first video is the main build, and the second is the re-building of it into a fixed bias amp with easy bias adjusting control, higher b+ and all that needed to be changed for it to double output power with lower dist. And it gets tested for clip-point on a scope.
It is an amateur that is having fun, the build don't look very nice but its charming when it plays fcking great..eheh
Also it is dangerous for kids and such since it is not fully covered up, having 425 volts ready for anyone with a finger to touch. So it stays in my 'workshop' with 8 guitars and at least that many guitar amps.
For someone building their first tube preamp / buffer , I highly recommend they see if they can find a ecc86 ( 6gm8 ).
This is a low voltage tube , that has a maximum plate voltage of 30 Vdc .
Any voltage above 48 Vdc , can be lethal , so tracking down 6gm8's may be well worth the effort .
The concept I used is a cathode follower with a the CCS that sets the bias current.
The great surprise is how much the CCS affects the sonics. After building a number of versions of CCS,
my favourite by far is made by back to back MPSA18 's.
The one draw back to this circuit is that a tube takes about 12 seconds to warm up , and this is mixed in with transistors ,
so Vout hits one of the voltage rails until the triode warms up .
However, only 1 ecc86 ( 6gm8 ) is needed for both the L and R channel .
However, I haven't tried a tube CCS , but a pentode is required for this .
IMO where the Q point is on the load line , has quite an effect on the sonics .
Pushing an ecc86 ( 6gm8 ) with a plate voltage up to 26Vdc and I = 5.6 mA sounds pretty good .
.
This is a low voltage tube , that has a maximum plate voltage of 30 Vdc .
Any voltage above 48 Vdc , can be lethal , so tracking down 6gm8's may be well worth the effort .
The concept I used is a cathode follower with a the CCS that sets the bias current.
The great surprise is how much the CCS affects the sonics. After building a number of versions of CCS,
my favourite by far is made by back to back MPSA18 's.
The one draw back to this circuit is that a tube takes about 12 seconds to warm up , and this is mixed in with transistors ,
so Vout hits one of the voltage rails until the triode warms up .
However, only 1 ecc86 ( 6gm8 ) is needed for both the L and R channel .
However, I haven't tried a tube CCS , but a pentode is required for this .
IMO where the Q point is on the load line , has quite an effect on the sonics .
Pushing an ecc86 ( 6gm8 ) with a plate voltage up to 26Vdc and I = 5.6 mA sounds pretty good .
.
Last edited by a moderator:
So here is a load line calculator , which I highly recommend people try .
https://www.vtadiy.com/loadline-calculators/loadline-calculator/
For a 6gm8 , setting the plate voltage to 26 Vdc , using the load line calculator , a good bias current looks to be about 2.35 mA .
But the cathode follower circuit with a CCS sounds great when the bias current pushed up to 5.6mA .
Any ideas what is going on ?
Also recall , the small signal parameters for a triode change with the bias current .
Data sheets provide a graph of the small signal parameters for a ecc88 / 6922 ,
but I can't find a graph of the small signal parameters for a ecc86 ( 6gm8 ) .
.
https://www.vtadiy.com/loadline-calculators/loadline-calculator/
For a 6gm8 , setting the plate voltage to 26 Vdc , using the load line calculator , a good bias current looks to be about 2.35 mA .
But the cathode follower circuit with a CCS sounds great when the bias current pushed up to 5.6mA .
Any ideas what is going on ?
Also recall , the small signal parameters for a triode change with the bias current .
Data sheets provide a graph of the small signal parameters for a ecc88 / 6922 ,
but I can't find a graph of the small signal parameters for a ecc86 ( 6gm8 ) .
.