Greetings Frank,
Its great to see you post again. Make no mistake I like the 8417's but having to watch them waiting for them to go wackos takes the fun out of any serious listening. Have you played with the 6BG6GA's that SY put us on to? I think it sounds punchier that a 6L6GC and the price cannot be beat.
Highfilms
Can you post the schematic of your modified 8417? I would like to see the changes that have been made.
Its great to see you post again. Make no mistake I like the 8417's but having to watch them waiting for them to go wackos takes the fun out of any serious listening. Have you played with the 6BG6GA's that SY put us on to? I think it sounds punchier that a 6L6GC and the price cannot be beat.
Highfilms
Can you post the schematic of your modified 8417? I would like to see the changes that have been made.
Hi,
The only time I toyed with the 6BG6s was when they came with an old Mac Intosh amp.
Excellent bass performance but HF performance let me down a little.
Of course it was probably not due to the tubes though.
Cheers, 😉
The only time I toyed with the 6BG6s was when they came with an old Mac Intosh amp.
Excellent bass performance but HF performance let me down a little.
Of course it was probably not due to the tubes though.
Cheers, 😉
Unfortunately, I don't have a schematic for the mods that have been done. That was done before I got them. I did however take some close up pics - I will try to figure out how to post them here so you can have a look.
I just want to be able to try some different tubes for different tones but I want to make sure I'm buying the right ones and not causing any damage.
Thanks.
I just want to be able to try some different tubes for different tones but I want to make sure I'm buying the right ones and not causing any damage.
Thanks.
I just looked at those 6BG6GA tubes. Do they all come with an adapter and that crazy looking plug on the top? Are those the tubes you are talking about? Is that adapter needed for all applications are can you just plug, bias, and play?
You will need the adapter unless you would like to rewire the sockets and drill a hole for the plate(high voltage wire and cap).
If you do that you will be using the 6BG6GA's only. The adapters are very easy to put together and will allow you to use the tube and then switch to say 6550's,KT88's,KT90's,EL34's, and 6L6's.
What tubes are being used other than the output tubes and the two 5AR4's?
If you do that you will be using the 6BG6GA's only. The adapters are very easy to put together and will allow you to use the tube and then switch to say 6550's,KT88's,KT90's,EL34's, and 6L6's.
What tubes are being used other than the output tubes and the two 5AR4's?
Each amp has 2 Sovtek 5881s - 2 Tesla ECC 83 and 2 GE 5AR4 rectifier tubes. I also have the solid state rectifier caps that can take the place of the 5AR4s. Here are a couple of pics of the insides. Maybe someone can give me a clue to see if the 5881 mod was done correctly or at least what tubes could be run in these beasties.
Thanks.
Thanks.
Years ago I owned a pair of Quicksilver KT88 amps that I bought new. At the time, I called Mike Sanders and asked him for a schematic and he told me that he never put it down on paper and so couldn't provide it. So I drew my own. The trim pot on the second tube establishes the bias for the driver tubes. Adjust for equal voltage on the drivers.
Osprey,
What tubes are used for the input and phase inverter, 12FQ7s? Nice schematic drawing by the way! Do you have the power supply drawn as well?
Craig
What tubes are used for the input and phase inverter, 12FQ7s? Nice schematic drawing by the way! Do you have the power supply drawn as well?
Craig
Quicksilver power supply
Note the 1st cap is way too big.
After looking at the KT88 schematic that was posted it would seem that the one I tried to hand draw a number of years ago had some errors. The schematic looks like what I had in my KT88 amp. Some resistor values are a little different possibly due to me measuring values in circuit or my cheap meter.
Note the 1st cap is way too big.
After looking at the KT88 schematic that was posted it would seem that the one I tried to hand draw a number of years ago had some errors. The schematic looks like what I had in my KT88 amp. Some resistor values are a little different possibly due to me measuring values in circuit or my cheap meter.
Attachments
Burnedfingers,
I thought the same thing when I saw the schematic, it's the same thing I came up with when I used your photos to figure out the circuit. Both input tubes ARE 12FQ7s? Measuring 1 percent resistors in circuit you might be off a tad, all depends on the circuit though. As far as the power supply goes does yours have the SS rectifiers in it along with the GZ34s?
Craig
I thought the same thing when I saw the schematic, it's the same thing I came up with when I used your photos to figure out the circuit. Both input tubes ARE 12FQ7s? Measuring 1 percent resistors in circuit you might be off a tad, all depends on the circuit though. As far as the power supply goes does yours have the SS rectifiers in it along with the GZ34s?
Craig
Hi Craig,
I sold it a while back and wish I had it still. It had been modified with the diode circuit. The belief is that they took most of the strain off the 2) 5AR4's while still allowing the slow warm up. I do this with every amp now. To be honest I cannot remember what mine had in it for input tubes. It did sound quite good and mine had 750 or 850 mfd cap for the second cap in the power supply. It had some bass for a 60 watt mono block.
I sold it a while back and wish I had it still. It had been modified with the diode circuit. The belief is that they took most of the strain off the 2) 5AR4's while still allowing the slow warm up. I do this with every amp now. To be honest I cannot remember what mine had in it for input tubes. It did sound quite good and mine had 750 or 850 mfd cap for the second cap in the power supply. It had some bass for a 60 watt mono block.
Yes, my amps had the dual GZ34s and 12FQ7 front end tubes. I have to credit this amp with my present huge stock of GZ34s and GZ37s which I retained when I sold the amp. I had a horrible time with rectifier tubes because of that huge first PS cap. In the end, I found that the GZ37s bought from Ned Carlson for $16 ea. were the answer and I bought enough to re-tube both amps.
I wouldn't want to have to buy those rectifier tubes today!
I wouldn't want to have to buy those rectifier tubes today!
Hi,
The GZ37 or CV#7?? something were the answer to the problem
with that amp.
Especially the ones with the 800microF input caps.
To the GZ34's credit, it's amazing they'd survive such start up sequences at all....😱
Joe, I'm pretty certain your amp had the typical 12FQ7s. Should not ever ever have sold it though.
An American classic.
Cheers, 😉
The GZ37 or CV#7?? something were the answer to the problem
with that amp.
Especially the ones with the 800microF input caps.
To the GZ34's credit, it's amazing they'd survive such start up sequences at all....😱
Joe, I'm pretty certain your amp had the typical 12FQ7s. Should not ever ever have sold it though.
An American classic.Cheers, 😉
Frank,
You are correct I should have held onto it. I am wondering if I can convert my 8417 to the KT88 circuit. I have the 12Fq7's and the KT88's. I am sure the output transformer is the same impedance as the 8417 transformer is. I cannot remember if the 8417 amp has a 12 volt heater supply. I could be wrong but I am thinking it has.
You are correct I should have held onto it. I am wondering if I can convert my 8417 to the KT88 circuit. I have the 12Fq7's and the KT88's. I am sure the output transformer is the same impedance as the 8417 transformer is. I cannot remember if the 8417 amp has a 12 volt heater supply. I could be wrong but I am thinking it has.
If it doesn't have a 12V heater supply just use the 6CG7/6FQ7 instead. The 8417 front end wouldn't have enough drive to be practical with the KT88s so a change of output tubes requires the change in front end topology too.
Actually the 8417 front end will drive KT88's without a problem. Checking the signal with the scope it has plenty of drive to run the output stage to full power without clipping the driver stage.
Hi,
Joe,
I forgot you had two sets of Quickies....😎
The 8417's definitely run from a 6.3V supply though.
You can convert to KT88 (any good ones around still?) or,...I'm sure they're all gone to tube heaven by now, the exceptionaly musical good ole' RCA 6550s.
In all honnestly, I'll really need to dig deep in my audio archives to find out what to do to make it work but I'm positive it can be done.
Cheers, 😉
P.S: I haven't followed the tube market for several years so I can only tell what was sounding good back in say 2000 but not nowadays.
Joe,
I forgot you had two sets of Quickies....😎
The 8417's definitely run from a 6.3V supply though.
You can convert to KT88 (any good ones around still?) or,...I'm sure they're all gone to tube heaven by now, the exceptionaly musical good ole' RCA 6550s.
In all honnestly, I'll really need to dig deep in my audio archives to find out what to do to make it work but I'm positive it can be done.
Cheers, 😉
P.S: I haven't followed the tube market for several years so I can only tell what was sounding good back in say 2000 but not nowadays.
Trying to source some resistors and I cannot find 44.2K and 53.6K that are 1 watt. Also I cannot find 17.5K 2 watt.
Substitute a CCS for the 17.5k resistor, then you can have both plate resistors be equal- 47k will work fine.
Otherwise, you can make those values from paralleled resistors. The absolute value of the plate resistors isn't important (within reason), they just need to be 10% or so apart to make up for the not-so-long tail. You can also make both plate resistors 51k, then parallel the one that needs to be smaller with a 1M trimmer. Adjust the trimmer for best balance (or lowest 2nd harmonic). The 17.5k can be a 20k in parallel with a 120k.
Otherwise, you can make those values from paralleled resistors. The absolute value of the plate resistors isn't important (within reason), they just need to be 10% or so apart to make up for the not-so-long tail. You can also make both plate resistors 51k, then parallel the one that needs to be smaller with a 1M trimmer. Adjust the trimmer for best balance (or lowest 2nd harmonic). The 17.5k can be a 20k in parallel with a 120k.
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