I was listening to crystal clear music only to have it interupted by some nasty sounding static and noise. I traced this down to a Mica? small value cap on pin 3 of the output tube socket. I had a small value cap rated at 600volts so I replaced it to see what happens. It was clean sounding again.
Question :
Anyone know the value of this cap, I haven't seen one of these in over 40yrs. It looks like it has been hot and I can't read the paint dot scheme that would probably tell me what the heck it was. The schematic looks like it shows 100UF or is it PF?
Also there is a 5K resistor shown in the feedback on the schematic and their is a 562 ohm in the amp.
Any help would be appreciated.
Joe
Question :
Anyone know the value of this cap, I haven't seen one of these in over 40yrs. It looks like it has been hot and I can't read the paint dot scheme that would probably tell me what the heck it was. The schematic looks like it shows 100UF or is it PF?
Also there is a 5K resistor shown in the feedback on the schematic and their is a 562 ohm in the amp.
Any help would be appreciated.
Joe
Joe,
If you can't post the schematic can you tell us what the output tube is? It would then be possible to determine the function of the cap and possible values from the pin connections...
(i.e. if pin three is the cathode, 100uf would be ok as a cathode bypass, but if pin three was the anode, then with 100uf you wouldn't be hearing anything!)
If you can't post the schematic can you tell us what the output tube is? It would then be possible to determine the function of the cap and possible values from the pin connections...
(i.e. if pin three is the cathode, 100uf would be ok as a cathode bypass, but if pin three was the anode, then with 100uf you wouldn't be hearing anything!)
Frank
Yup its a 562ohm 1% nasty looking black resistor about the thickness of my little finger and I would assume its a 3 or 5 watt job. The resistor is going to be replaced per the 8417 conversion guide that was on the board a while back. I think I will use somewhere around 270 ohm.
I wasn't able to purchase a mica capacitor but did snag a 100pf/600volt film to replace the original.
What are the correct values of the resistors on the cathode of the 12AX7 to ground? I think I can see a 820 but the other value is blurred on my schematic.
Any suggestions for hot rodding this garage amp?
Per Mike at Quicksilver the impedance of the output transformer is Quote "Closer to 3900 ohms" not 4200ohms.
The schematic I posted looks much better than what printed off for me.
Joe
Yup its a 562ohm 1% nasty looking black resistor about the thickness of my little finger and I would assume its a 3 or 5 watt job. The resistor is going to be replaced per the 8417 conversion guide that was on the board a while back. I think I will use somewhere around 270 ohm.
I wasn't able to purchase a mica capacitor but did snag a 100pf/600volt film to replace the original.
What are the correct values of the resistors on the cathode of the 12AX7 to ground? I think I can see a 820 but the other value is blurred on my schematic.
Any suggestions for hot rodding this garage amp?
Per Mike at Quicksilver the impedance of the output transformer is Quote "Closer to 3900 ohms" not 4200ohms.
The schematic I posted looks much better than what printed off for me.
Joe
Attachments
Bad news!
Actualy is the oposite...the feedback will be decreased...
The output transformer as more voltage gain in the 16 Ohms tap so the open loop voltage gain is greater..
When you change for the 8 Ohm tap the open loop voltage gain is reduced...so the feedback will be decreased...
Um abração!
Actualy is the oposite...the feedback will be decreased...
The output transformer as more voltage gain in the 16 Ohms tap so the open loop voltage gain is greater..
When you change for the 8 Ohm tap the open loop voltage gain is reduced...so the feedback will be decreased...
Um abração!
http://www.triodeel.com/8417.htm
The article (8417.htm) explains how to convert a 8417 to use 6550's. Http://WWW.triodeel.com/8417.htm
It makes mention to the 562ohm resistor in the feedback loop. If the 562 ohm resistor was the original part what changes would their have been to the 820 and 220 cathode resistors on the 12AX7?
Joe
The article (8417.htm) explains how to convert a 8417 to use 6550's. Http://WWW.triodeel.com/8417.htm
It makes mention to the 562ohm resistor in the feedback loop. If the 562 ohm resistor was the original part what changes would their have been to the 820 and 220 cathode resistors on the 12AX7?
Joe
Thanks Frank
You know of the condition of this pair of 8417's that I have. I'm sure they have had their share of little hands in them. If you say its a 5K I will change them to 5K resistors. This does answer my questions as to why the 220ohm resistors had been changed to a different value.
Frank
I have set number three of mono block Quicksilvers headed my way. These are virgins and have extra 8417 tubes. I guess I'm stuck on them.
Joe
You know of the condition of this pair of 8417's that I have. I'm sure they have had their share of little hands in them. If you say its a 5K I will change them to 5K resistors. This does answer my questions as to why the 220ohm resistors had been changed to a different value.
Frank
I have set number three of mono block Quicksilvers headed my way. These are virgins and have extra 8417 tubes. I guess I'm stuck on them.
Joe
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