8417 Tube Sound Question

TubeSocket

Active Member
I am eying an 8417 100W amp. I would like to use the amp to play my bass guitar through at the lower volume gigs. Now, the amp comes with 2 8417's installed but I have no idea if they are any good or not until I get them in my hot little hands.
so...

While working with a PA in our church's gym I came a cross a little brown bag- inside lay three treasures: 2X RCA 8417 and 1X 7199. Still rubber banded together since the day they were purchased in the late 80's. NOS in beautiful factory boxes in other words. Long story short, the amp that uses them is not going to last long enough to finish off the tubes in it so these babes are mine (I have permission).

Now... I am asking if these RCA 8417's have some sort of "wow factor" to them smiler to say a NOS RCA 6l6. Ya know... that magic tube vibe if you will. I ask because I am considering dumping these (I would have 4 if the ones in the amp are good) and just buying a good NEW KT88 duet. The sale of these tubes would also help fund the restoration. (Bias alterations included)

So...

Dump em?

Run em?
 
8417 tubes ar no longer made, and in VERY short suppy. If you find any, expect to pay premium prices. A pair usually goes for $100 or more. I'd consider selling what you have, and using the profits from them to get a nice 6L6 or EL34 amp for using as a guitar amp. EL34's distort better and sound warmer.

I've got a couple monoblocks that were made to use them, but were converted by the factory for EL34 tubes because of the lack of 8417's
 
The 8417 is a great sounding hifi tube IMO. As far as I'm aware, only Sylvania and GE actually made them and there was cross branding. I run them in Bogen MO-100As and M120s. As simi says, they are no longer in production but do come up for sale not infrequently - they do have good resale value.
 
Yeah should have specified the intent a little better...
I am going for lots of clean power in a small (medium sized iron) package; hence why I was looking at the KT-88.

The amp I am eying looks to be almost NOS so the transformers should be nice and healthy. Because of the 100 watt output, I am really looking to make this into a little sleeper amp with my own tone circuit installed. Say... the one I built from an old Ampeg schematic.

I know the 84's aint made any more and the ones that were had to compete with the new transistors. Hence companies drove the socks off of them and wondered why they failed.

I completely rebuild all of the tube amps that come my way both for safety and the fact that I use them. I am also looking to get into some more mods instead of simply restoring these to factory PA specifications.
so... More of what I am trying to do...

The amp would see at least 7 hours of actual play time per week. Perhaps with idle time it would be about 10 hours a week. I am no NOS tube expert, but I would imagine that the brand new 8417's I have would not hold that kind of use for more than 2 or 3 years. (I play at sane levels) Then I would be left with tubes that cost even more than they do right now!

So, unless these are total tone and life sleeper tubes, I would not mind seeing them go. I would be rebuilding the amp in the process so the conversion is a non-issue.

This is really more of an 8417 tone question and if that tone justifies the price that these tubes command... Please keep in mind that I would rebuild the amp with metal film flameproof resistors and orange drop 716 caps along with JJ can caps and CTS pots. Nothing magical. I DO like the sound that new stock tubes produce in my amps AFTER they have been rebuilt.

Lastly, NOS 6l6 or el34 are just about as much and they don't have the power these tubes do either...

Sorry, I know this not a music forum. Musicians do not usually know the stuff I like to talk about. They pay too much for their gear anyway! I satisfy both of my urges this way! Tubes AND economy!
 
I have no clue how they would sound for a guitar amp, but like Tinkerbelle said, they sound fantastic in Hi-Fi use from what I understand. I can't say I've ever seen a guitar amp use them, so that may be a clue?
 
I have only read about a few obscure manufacturers that did use them. I do like the hi-fi sound though. I don't think that tube hung around long enough for the musical industry to adopt it.
 
I have no experience with the tube for guitar amp use. However, as a reference the following article does give some audio listening impressions vs. many other high power output tubes. It's a little dated, so the new production tubes may well have improved from the time of this article but it may give you some input vs. old production tubes.

http://www.audioasylum.com/forums/otl/messages/526.html

If the two used 8417 tubes are good you may want to consider recapping then giving it a listen with 8417 tubes to form your own opinion, before considering re-biasing for KT88 or EL34.
 
I just finished rebuilding a Guild Quantum X Thunderbass amp that uses a pair of 8417s. I love the tone, and the amp's owner is really excited about it. Properly biased and with 550 volts on the plates, it made my little 12" Jensen test speaker whimper then beg for mercy. The owner now has it properly hooked up to a pair of 15" EVMs and it is happy.

The main thing to be careful of when using 8417s is to keep the screen voltage no higher than 300V. To accomplish this in the Guild, they used a 6GF7A (dissimilar triode) specifically to regulate the screen voltage to the power tubes. A cool design and an extremely stable result.

I hope you go for it - I really fell in favor with this tube and you might too. I can't imagine having used anything else. Guild 's designer in the 60's, Aaron Newman claimed it was built for 6550s, and they did make a version with 6L6s, but the 8417 was a great choice.
 
Wow- he seems to really speak highly of the 8417. I wonder if I should get my hands on some new Sovtek KT88's, install an adjustable bias and see what happens between those and my new 8417. (Tinkerbelle's advice)

Can I just throw the KT-88's in with just a bias adjustment? I do not have a schematic yet. All I know is it is 4 channel, 100W output with 2X 8417 tubes.

Assuming the rest of the amp is healthy for atleast some testing..
 
Can I just throw the KT-88's in with just a bias adjustment?


I realize sometime in the last 8 years the OP has probably gotten his answer, but not quite. The KT88 would need a fair bit more negative voltage for one, probably well beyond what the stock bias supply can offer. I want to say my amp running KT tubes needs about -45 volts, where the original 8417's that would have been in that spot were probably closer to -20.

The KT88 also wants a lot more drive to make full power. With bias mods a KT88 will make some sound where an 8417 was, but I would not expect the stock driver stage to be able to run it to full power. Not to say the driver can't be re-worked to make it all go, it just is not likely to do it stock. I don't have datasheets in front of me, but they will tell you what the grid to grid voltage is to get full power out of each. Its probably about double the voltage for the KT88.
 
I realize sometime in the last 8 years the OP has probably gotten his answer, but not quite. The KT88 would need a fair bit more negative voltage for one, probably well beyond what the stock bias supply can offer. I want to say my amp running KT tubes needs about -45 volts, where the original 8417's that would have been in that spot were probably closer to -20.

The KT88 also wants a lot more drive to make full power. With bias mods a KT88 will make some sound where an 8417 was, but I would not expect the stock driver stage to be able to run it to full power. Not to say the driver can't be re-worked to make it all go, it just is not likely to do it stock. I don't have datasheets in front of me, but they will tell you what the grid to grid voltage is to get full power out of each. Its probably about double the voltage for the KT88.

The difference in drive voltage, is actually almost exactly the same ratio as the difference in bias voltage- for primarily the same reasons,. So, yes, they do need like just over 2x the drive voltage from the front-end and inverter stages.

Regards,
Gordon.
 
I've switched out 6550's (KT88) for the stock 8417's in my Dynaco MK VI's some years ago with excellent results. All I did was change the bias circuit a little bit, nothing more, and the amps sounded fantastic.
 
I'd be curious to see what it did for power testing. No idea what the Mark VI used, but its possible that it had enough kick to drive them to full output.

My Bogen MO-100A's originally ran a single 7247 for the driver to feed four 8417 output tubes. It now uses a single 6AN8 to feed a pair of KT120 (or KT88, 6550, etc) to full power. The driver is now capable of a whole lot more voltage swing than the original. Dave's testing on the stock design actually found that even it was barely able to get the job done with the stock tubes, absolutely no chance of it driving a lower mu tube properly.

My Fisher TA-600 with it's 18 watt per channel 7189 output stage uses a virtually identical driver stage to the stock Bogen 100A. Thats how easy the 8417 was to drive.
 
In the early 70's, a company out of Milwaukee called "Eros", built PA heads for bands. They bought Dynaco MK VI's from Dynaco, retubed them with 6550's, put two of them in the head connected to a multichannel mic. preamp, and called them 500 watt heads. The band I traveled with had one. I never measured the output as the thing never went down in the time I was with them, but it was loud and powerful, driving a couple of boxes 5 or 6 feet high with a pair of Altecs, as well as an Altec horn on the top, times two, one for each side of the stage. At the time I was told the company bought the last of the MK VI amps from Dynaco.
 
In the early 70's, a company out of Milwaukee called "Eros", built PA heads for bands. They bought Dynaco MK VI's from Dynaco, retubed them with 6550's, put two of them in the head connected to a multichannel mic. preamp, and called them 500 watt heads. The band I traveled with had one. I never measured the output as the thing never went down in the time I was with them, but it was loud and powerful, driving a couple of boxes 5 or 6 feet high with a pair of Altecs, as well as an Altec horn on the top, times two, one for each side of the stage. At the time I was told the company bought the last of the MK VI amps from Dynaco.

A Mk VI could be re-tweaked in the front end, to drive 6550s. It had a 7199 driver- essentially the same type and performance tube as the 6AN8 that Dave G. used in the Bogen MO-100, as described above- which, if tuned right, can definitely be made to adequately drive 6550s...

Regards,
Gordon.
 
Back in the 60s, I was growing up in Indianapolis, which history has shown was the center of the garage band phenomenon of that day. I too was in one of the better bands of the day in that town, and back then, the PA amplifier of choice was almost always a Bogen MX-60A. We used our own home-made equipment, while for the bands using the Bogen, it was well known for its pulsing and pumping, distorted sound when pushed too hard. Much later in life, I found out what the cause of that was (mentioned in my MO-200A thread), but it did use a pair of 8417s, which to their credit, seemed to withstand the band environment pretty well. Remember however that these bands had no rodies. Everybody in the band owned their own equipment as well as the community equipment of the band, so equipment was not usually subjected to the rigors that equipment on the road sees today. For maximum dependability however (and power output), the 6550 is a much tougher tube physically, with the 6L6GC being top dog dependability wise. Unbelievable what that tube could take, being the very essence of a Timex watch........

Dave
 
Back in the 60s, I was growing up in Indianapolis, which history has shown was the center of the garage band phenomenon of that day. I too was in one of the better bands of the day in that town, and back then, the PA amplifier of choice was almost always a Bogen MX-60A. We used our own home-made equipment, while for the bands using the Bogen, it was well known for its pulsing and pumping, distorted sound when pushed too hard. Much later in life, I found out what the cause of that was (mentioned in my MO-200A thread), but it did use a pair of 8417s, which to their credit, seemed to withstand the band environment pretty well. Remember however that these bands had no rodies. Everybody in the band owned their own equipment as well as the community equipment of the band, so equipment was not usually subjected to the rigors that equipment on the road sees today. For maximum dependability however (and power output), the 6550 is a much tougher tube physically, with the 6L6GC being top dog dependability wise. Unbelievable what that tube could take, being the very essence of a Timex watch........

Dave
I was the manager, roadie, car owner, and finance director of the bands in the early 70's. I actually got an equal share. I built one of the first mixer boards for us. No one up here had seen one or was using one at the time. They just turned everything up to 11 until I came along and turned them down.
 
The "sound" of a tube (assuming that such thing exist) is mostly dependant on the circuit topology in wich it is used, and many other external factors. My personal experience with the 8417 revealed that it "sounded" wonderfully in my FISHER SA-1000 , just so-so in a DYNACO MK VI and like crap in a BOGEN P.A amp. Thus (IMO) it is quite impossible to characterize a typical 8417 "sound" especially when used (overdrived ?) in guitar amps, an application where it was never (or rarely ?) used.
The 8417 become scarce and expensive and there are no plans for a re-issue, it is a very peculiar last-generation tube for which there are no (electrically compatible) direct substitutions. All good reasons to avoid using this tube in any new design, except if you have a big pile of N.O.S 8417's in your stash.
 
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