[DaveC113]

Josh, thats pretty cool...it will look like an antique with the topsheet patina like that.

I've been thinking about adding some ventilation holes, but its not that hot and I'm very lazy. It feels hot, but I can leave my hand there without it getting painful... 

Also, I may hardwire it in triode mode with no cfb... I did try cfb, and it sounded really bad, much worse than I was expecting. I guess I was expecting a more sterile sound with less overall distortion with cfb, but it sounded muddy and the bass was bloated. Also, I've tired of UL, triode sounds more natural and I don't need the extra power. I am using the amp with Omega XRS single drivers, maybe less "amplifier-friendly" speakers would react differently and UL and/or cfb might be preferable? I now have 2 switches on my amp that I'll probably never use again, something to think about... maybe wire the switches but don't install them in the chassis until you're sure you want them...

Also, I just put in some Genelex kt88 re-issues that jrebman loaned me. These are probably a good option, I'll have to let them burn in. So far the Tung Sol 6550 re-issues I was running are really, really good. Very holographic, 3D soundstage... the speakers just disappear. Tone is great, everything just sounds right. There isn't as much bloom or texture as the Genelex, but its a minor difference. I'm waiting for the Genelex's highs and soundstaging to open up, we'll see if that happens... 

[JoshK]

Dave,
This isn't a Simple SE amp, it is going to be an E-linear amp, ala Pete Millett.  D3A into a KT88 with the D3A in pentode mode and plate to plate feedback through the UL connection.  Of course it could migrate an any direction thereafter, but that is what it'll start out as.

Don,
The stuff I got to finish the plate I believe is semi-gloss.  Its a sort of wax.  I forget what it is called.

[JoshK]

Its called Renaissance wax polish.

[jeffdavison]

Need a bit o help with the circuit.... Have I done my homework? It makes sounds but not music.
Need constructive critisism, corrections etc....




Thanks..

JD

[BillB]

Here is what I came up with using your numbers in SE-Amp CAD:

Sorry about the file compression only have paint on the laptop.

[jeffdavison]

Bill,

Not quite sure you put all my numbers in .

Tranny is different as well as cap and resistor values, so I really don't know how to interperet or apply your model.

Also there is nothing showing the input and driver stages, which are also a very big concern at the moment also.

Thanks

Jeff

Here is what I came up with using your numbers in SE-Amp CAD:

Sorry about the file compression only have paint on the laptop.

[BillB]

I went with the first 3k tranny I could find and using your resistance and B+ numbers that is what the program inserted for caps.

Sorry about the input stage, this only does the SE side.

[DaveC113]

I'm guessing you're using resistors at the base and emitter of the ccs that are not shown on the diagram?

[jeffdavison]

the CCS for the 6SN7 uses a 470R to set the 7ma. (and a 1K off the G terminal) , the CCS for the 6H30 uses a 100R to set the 19ma. (and a 1K off the G terminal)

JD

[DaveC113]

ok, but it looks like 100r will give more like 25 mA (looking at the chart on the ixys datasheet)... minor issue though. I can't see anything obvious... maybe check the signal between stages to try to narrow down where the issue is?

also, isn't the 3rd screen usually connected like this?:



Dave

[jrebman]

Can you be a bit more specific about the sonics?

Without being able to see the schematics, I'm guessing that the problem lies somewhere between the 6sn7 and the 6h30. Possibly the wrong type of attenuator?

First things I myself would try would be to lose the CCS on the 6sn7 and wire a pot as in the kit2 schematic.

If you're using CFB, take that out as well -- you will not need it with the Silk transformers.

FWIW

-- Jim

[jeffdavison]

Dave,

the 100R inputs the 6550 at pin 5,

the 100R drid resistor is from pin 4 to the mode select switch.

Drawing is a bit misleading, but the pins are correct.

ok, but it looks like 100r will give more like 25 mA (looking at the chart on the ixys datasheet)... minor issue though. I can't see anything obvious... maybe check the signal between stages to try to narrow down where the issue is?

also, isn't the 3rd screen usually connected like this?:



Dave

[jeffdavison]

Sound is very distorted, perhaps I blew the output transformer? I accidently inhte very early testing put a 720 voltage where I thought it was a 360. ( a big boo boo about center taps and the use of Greatz bridges..)

The CCS on the 6SN7 is like Pimms example, with a little more juice..http://www.pmillett.com/current_source.htm

Can you be a bit more specific about the sonics?

Without being able to see the schematics, I'm guessing that the problem lies somewhere between the 6sn7 and the 6h30. Possibly the wrong type of attenuator?

First things I myself would try would be to lose the CCS on the 6sn7 and wire a pot as in the kit2 schematic.
It already is except the 220K aftwards instead of the 470K
Jeff


If you're using CFB, take that out as well -- you will not need it with the Silk transformers.

FWIW

-- Jim

[jrebman]

Well, that certainly can't help anything, but if it were only a brief exposure to the higher voltage, most transformers can usually withstand 2kv between windings, so it is unlikely that you have a short between windings -- but I suppose anything could happen.  Did you make any basic resistance measurements on the transformers to see if there was anything obvious?  This won't always eliminate a problem if they check out, but it's a place to start.

My wild and wooly guess is that perhaps you are overdriving the grid of the 6h30 and making it behave like a diode and clamping part of the waveform.  Again, only one possible explanation.

If you've got a scope, I'd get in there *carefully* and start looking at various points along the signal path.

That's about all I can really offer without being able to see the schematic, so I'll have to let the more experienced guys chime in here.

Good luck -- at least there were no pyrotechnics .

-- Jim

[jeffdavison]

Sent you the full shems via email.

I'm too novice yet about having or using a scope to check circuitry.

Resistance measurements are about the same across the winding comparing each transformer to the other on the primary and secondary sides. If I had a virgen set I could compare against it. I do have another pair in transit to build another amp. I need to debug this one first before I start that one.

Jeff

Well, that certainly can't help anything, but if it were only a brief exposure to the higher voltage, most transformers can usually withstand 2kv between windings, so it is unlikely that you have a short between windings -- but I suppose anything could happen.  Did you make any basic resistance measurements on the transformers to see if there was anything obvious?  This won't always eliminate a problem if they check out, but it's a place to start.

My wild and wooly guess is that perhaps you are overdriving the grid of the 6h30 and making it behave like a diode and clamping part of the waveform.  Again, only one possible explanation.

If you've got a scope, I'd get in there *carefully* and start looking at various points along the signal path.

That's about all I can really offer without being able to see the schematic, so I'll have to let the more experienced guys chime in here.

Good luck -- at least there were no pyrotechnics .

-- Jim

[jeffdavison]

full schmatic



JD

[andrewbee]

Either your diagram or pin numbers are incorrect.
You are feeding your signal into the incorrect screen on the output tube. Your diagram shows the signal being fed to G2. The signal should be fed into G1. G2 is where the UL tap would go.

Connections should be.
pin 1 is connected to the outer metal base (internal)
pin 5 is your G1
pin 4 is G2
pin 3 is plate / anode
pin 8 is your cathode
pins 2 & 7 are your heaters
pin 6 has no connection

The basing of the 6550 is 7AC. You need to double check everything.

[JoshK]

Yeah, as Andrew said, you are screen driving the output tube according to that diagram, which requires very different bias points and a different tube.  I am not sure the 6550 can be screen driven nicely.  3K is also pretty low for a 6550 I think.  We are using 5K typically. 

Have you checked voltages?  Did you check the PSU voltages?

[jeffdavison]

ok,

don't look at anything inside the 6550 "circle" It's the pins that tell how the circuit is wired.

checked voltages with all tubes being driven.

B+ to the 6550 / OPT Traffo is +400 to + 420 (depending on which rectifier I use....5V4g, 5AR4, GZ32
B+ to the top of the 6SN7 CCS is +300
B+ to the top of the 6H30 CCS is +210

JD

Yeah, as Andrew said, you are screen driving the output tube according to that diagram, which requires very different bias points and a different tube.  I am not sure the 6550 can be screen driven nicely.  3K is also pretty low for a 6550 I think.  We are using 5K typically. 

Have you checked voltages?  Did you check the PSU voltages?

[jeffdavison]

Andrew... here's the corrected 6550 internals. Pins are connected to rest of circuit are the same.



Jeff

Either your diagram or pin numbers are incorrect.
You are feeding your signal into the incorrect screen on the output tube. Your diagram shows the signal being fed to G2. The signal should be fed into G1. G2 is where the UL tap would go.

Connections should be.
pin 1 is connected to the outer metal base (internal)
pin 5 is your G1
pin 4 is G2
pin 3 is plate / anode
pin 8 is your cathode
pins 2 & 7 are your heaters
pin 6 has no connection

The basing of the 6550 is 7AC. You need to double check everything.