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Got my SFDR last night need advice on...

9/2/1999 6:40 PM
pHiL	Got my SFDR last night need advice on... tube placement. The previous owner very carefully removed the tubes before shipping, wrapping them in bubble wrap and put them in the back of the amp. My problem is this. It appears that some of the preamp / vib/ rev / driver tubes have been substituted so I haven't fire it up until I know which position they should most like go. To pin it down mainly the Philips 12AX7A/7025A(what is it really?) and the Siemans ECC81. Enter Ampage to the rescue! The tube chart reads: 5U4GB - 6V6 - 6V6 - 12AT7 - 12AX7 - 7025 - 12AT7 - 7025 - 7025 With the tubes that were supplied I'm guessing they should be positioned as follows. I'm also indicating mfr. 5U4GB(RCA) - 6V6(SYL) - 6V6(SYL) - 12AT7(RCA) - 12AX7(JOLIDA) - 12AX7A/7025A(PHLPS) - ECC81(SMNS) - 7025(RCA) - 7025(RCA) I'm planning on taking this into my amp tech next week but I would still like to be able to fire it up and get the best out of it if possible with the existing tubes without damaging anything. Any suggestions? Thanks, pHiL

9/2/1999 6:40 PM

pHiL

Got my SFDR last night need advice on...

tube placement.

The previous owner very carefully removed the tubes before shipping, wrapping them in bubble wrap and put them in the back of the amp.

My problem is this. It appears that some of the preamp / vib/ rev / driver tubes have been substituted so I haven't fire it up until I know which position they should most like go. To pin it down mainly the Philips 12AX7A/7025A(what is it really?) and the Siemans ECC81.

Enter Ampage to the rescue!

The tube chart reads:

5U4GB - 6V6 - 6V6 - 12AT7 - 12AX7 - 7025 - 12AT7 - 7025 - 7025

With the tubes that were supplied I'm guessing they should be positioned as follows. I'm also indicating mfr.

5U4GB(RCA) - 6V6(SYL) - 6V6(SYL) - 12AT7(RCA) - 12AX7(JOLIDA) - 12AX7A/7025A(PHLPS) - ECC81(SMNS) - 7025(RCA) - 7025(RCA)

I'm planning on taking this into my amp tech next week but I would still like to be able to fire it up and get the best out of it if possible with the existing tubes without damaging anything.

Any suggestions?

Thanks,

pHiL

9/2/1999 6:48 PM
Troy	Phil: Sounds like you've got it right! Just make sure you line the tube up right in the socket and in a circular motion gently insert the tubes. The positioning of the small pre-amp tubes is not as critical as the rectifier (largest tube 5U4) and the power tubes. The 5U4 goes on the end with the 6V6's beside it.

9/2/1999 8:51 PM
pHiL	Thanksf or the tip on installation but I've already installed the tubes and don't have a problem with inserting them in the sockets etc. It's just that the Philips 12AX7A/7025A and Siemens ECC81 were throwing me off since the tube chart actually calls for straight 7025 and 12AT7 respectively. I'm not familiar with the difference or interchangeability of 12ax7 for a 7025 or the ECC81 for a 12AT7. As i told the previous owner. Is it not possible that an amp tech would tweak a ckt to compensate for characteristics of a tube substitute? Probably not but one never knows. Also, since I'm probably going to have the thing serviced, I'm going to try and get as much info as possible to make a good choice on new or NOS tubes if they're needed. Again, any recommendations are welcome and thanks for the advice. pHiL

9/2/1999 8:51 PM

pHiL

Thanksf or the tip on installation but I've already installed the tubes and don't have a problem with inserting them in the sockets etc. It's just that the Philips 12AX7A/7025A and Siemens ECC81 were throwing me off since the tube chart actually calls for straight 7025 and 12AT7 respectively.

I'm not familiar with the difference or interchangeability of 12ax7 for a 7025 or the ECC81 for a 12AT7.

As i told the previous owner. Is it not possible that an amp tech would tweak a ckt to compensate for characteristics of a tube substitute? Probably not but one never knows.

Also, since I'm probably going to have the thing serviced, I'm going to try and get as much info as possible to make a good choice on new or NOS tubes if they're needed.

Again, any recommendations are welcome and thanks for the advice.

pHiL

9/2/1999 10:25 PM
Troy	Phil: I hope I didn't insult your intelligence on inserting tubes. The ECC81 is just the European designation for a 12AT7 (they're the exact same tube. The 7025/12AX7A is utilizing an old military designation of 7025 which is the same as a 12AX7. To my knowledge, in the glory days of tube usage, many companies offered a "lower noise" 12AX7 and called it a 7025. I like the old RCA 7025's, especially in Fender amps (in the first gain stage position; 2nd tube from the far end in the vibrato channel in your SFDR)! If the amp is sounding and working properly, I wouldn't worry with the preamp tubes too much, especially if you've got old RCA's in there. You could upgrade to RCA "blackplate" 6V6's for a subtle difference (better to me). Maybe try a 5V4GA rectifier for tighter low end too.

9/2/1999 10:25 PM

Troy

Phil: I hope I didn't insult your intelligence on inserting tubes. The ECC81 is just the European designation for a 12AT7 (they're the exact same tube. The 7025/12AX7A is utilizing an old military designation of 7025 which is the same as a 12AX7. To my knowledge, in the glory days of tube usage, many companies offered a "lower noise" 12AX7 and called it a 7025. I like the old RCA 7025's, especially in Fender amps (in the first gain stage position; 2nd tube from the far end in the vibrato channel in your SFDR)! If the amp is sounding and working properly, I wouldn't worry with the preamp tubes too much, especially if you've got old RCA's in there. You could upgrade to RCA "blackplate" 6V6's for a subtle difference (better to me). Maybe try a 5V4GA rectifier for tighter low end too.

9/2/1999 11:13 PM
pHiL	No offense taken. I've told many that I know just enough about electronics to be dangerous and I always keep a fire extinguisher handy {8^D The info about the ECC81 and 12ax7 vs 7025 is exactly what I was looking for. And I figured that someone would recommend the RCA blackplates but geez their expensive! I think I have a copy of Mook's 6v6 review laying around and will go back to it for possibly some good alternatives. Then there's also that lone Jolida Chinese 12ax7 in there and I've heard bad things about some of the Chinese tubes... maybe not. But at least I should be able to play through it tonight without screwing anything up.... where's that fire extinguisher! Thanks again, pHiL

9/2/1999 11:13 PM

pHiL

No offense taken. I've told many that I know just enough about electronics to be dangerous and I always keep a fire extinguisher handy {8^D

The info about the ECC81 and 12ax7 vs 7025 is exactly what I was looking for. And I figured that someone would recommend the RCA blackplates but geez their expensive! I think I have a copy of Mook's 6v6 review laying around and will go back to it for possibly some good alternatives.

Then there's also that lone Jolida Chinese 12ax7 in there and I've heard bad things about some of the Chinese tubes... maybe not. But at least I should be able to play through it tonight without screwing anything up.... where's that fire extinguisher!

Thanks again,

pHiL

9/3/1999 3:28 AM
Andrew McWhirter	Hi Phil, If you want to see people's recommendations for what tubes to put in a DR (preamp mainly) look for a post from me on dejanews - alt.guitar.amps group. I asked exactly that question. 5U4GB - 6V6 - 6V6 - 12AT7 - 12AX7 - 7025 - 12AT7 - 7025 - 7025 In a nutshell, advice I got is to put a good 12AT7 in the reverb driver position (the third from the right, looking in the back of the amp), because it gets driven pretty hard. I ended up buying a NOS JAN Philips 12AT7 for that position. The tremolo oscillator doesn't need to be a great tube (the 12AX7 on the chart, 5 from right). That's where I'd put the chinese tube. I happen to have some Ruby STR7025's stashed away that I'll use for the first preamp stage(s) (rightmost two tubes), but in currently available tubes it seems that folks like the new Sovtek 12AX7LPS, and the EI 12AX7's. There's also NOS JAN GE 12AX7's around for not too much $$. For the power tubes, I bought NOS JAN Philips 6V6GT's. I can't tell you how they sound since the amps not in one piece yet...(and I don't have anything to compare to anyway) Mook's taste test is probably a great place to start! I think I've read good things about the Visseaux and French Mazda 6V6's too (though they're a fair bit more than the Philips, IIRC). HTH! Andrew

9/3/1999 3:28 AM

Andrew McWhirter

Hi Phil,

If you want to see people's recommendations for what tubes to put in a DR (preamp mainly) look for a post from me on dejanews - alt.guitar.amps group. I asked exactly that question.

5U4GB - 6V6 - 6V6 - 12AT7 - 12AX7 - 7025 - 12AT7 - 7025 - 7025

In a nutshell, advice I got is to put a good 12AT7 in the reverb driver position (the third from the right, looking in the back of the amp), because it gets driven pretty hard. I ended up buying a NOS JAN Philips 12AT7 for that position.

The tremolo oscillator doesn't need to be a great tube (the 12AX7 on the chart, 5 from right). That's where I'd put the chinese tube.

I happen to have some Ruby STR7025's stashed away that I'll use for the first preamp stage(s) (rightmost two tubes), but in currently available tubes it seems that folks like the new Sovtek 12AX7LPS, and the EI 12AX7's. There's also NOS JAN GE 12AX7's around for not too much $$.

For the power tubes, I bought NOS JAN Philips 6V6GT's. I can't tell you how they sound since the amps not in one piece yet...(and I don't have anything to compare to anyway) Mook's taste test is probably a great place to start! I think I've read good things about the Visseaux and French Mazda 6V6's too (though they're a fair bit more than the Philips, IIRC).

HTH!

Andrew

9/3/1999 5:19 PM
Doc	If you need a copy of the original fender schematic, visit the Fender Amp Field Guide site. They have a SF DR diagram posted there. Tubes are numbered per their physical position on the chassis, and you can get a better idea of the function of each tube. Eventually, you'll understand the whole circuit. I'm not disagreeing on anyone's suggestions for which tube to use where, but I like to make sure there's a new or healthy US made 12AT7 in the driver/phase inverter position. The 12AT7 used for the reverb driver does come under some severe duty, but it's an auxiliary tube. Try any 12AT7 in that position, and check the reverb performance. If the reverb sounds good, then leave it in. The 12AX7s that are critical, as far as gain & noise characteristics, are the first two (V1 is normal channel which you may not use much and V2 is vibrato/reverb channel (which everybody uses), and the one just beyond the reverb driver transformer which is the reverb signal recovery amp. Well, that's my $.02. I bet it's going to be one of your favorite amps.

9/3/1999 5:19 PM

Doc

If you need a copy of the original fender schematic, visit the Fender Amp Field Guide site. They have a SF DR diagram posted there. Tubes are numbered per their physical position on the chassis, and you can get a better idea of the function of each tube. Eventually, you'll understand the whole circuit.

I'm not disagreeing on anyone's suggestions for which tube to use where, but I like to make sure there's a new or healthy US made 12AT7 in the driver/phase inverter position. The 12AT7 used for the reverb driver does come under some severe duty, but it's an auxiliary tube. Try any 12AT7 in that position, and check the reverb performance. If the reverb sounds good, then leave it in.

The 12AX7s that are critical, as far as gain & noise characteristics, are the first two (V1 is normal channel which you may not use much and V2 is vibrato/reverb channel (which everybody uses), and the one just beyond the reverb driver transformer which is the reverb signal recovery amp.

Well, that's my $.02. I bet it's going to be one of your favorite amps.

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