8417 vs. 6550 / KT88

[Blair]

These look like they are somewhat interchangeable. If this is the case. Has anyone ever bought a few old Bogen MO 100s or 200s for that matter and used the 6550s in them? They look like thay would make great high power monoblocks and the iron looks BEEFY!. Also note the bandwidth on those OPTs of something like 10hz-50K. Anyway, just thinking out loud and trying to blow money before I earn it again Yellow_Light_Colorz_PDT_02

Blair

[kheper]

These tubes are not interchangable. The
8417 puts out more watts than the kt88.

http://www.nj7p.org/Tube4.php?tube=8417

Most people who buy an old amp which ran
PP 8417s opt for changing the amp to PP
parallel kt88s. The 8417s are no longer in production.

The Dynaco MK VI used those tubes.

http://home.indy.net/~gregdunn/dynaco/c ... index.html

I've seen those Bogen amps on e-bay. They
are invariably grungy looking. Those amps
were PAs, and would probably need more
work than just setting up PP parallel kt88s.

[erichayes]

It's not that the 8417 put out more power (a pair of 6550s can do 100 watts), it's that the transconductance of the 8417 was so stinkin' high (23,000 µmhos), it took practically nothing to drive them to full output.

The downside was that in order to get that kind of performance, the elements had to be reeeal close together, which caused the tube to go into pyrotechnic mode fairly often.

I've only seen one pair of the Dynas, and the only thing original on them were the transformers and the tube sockets. They were running 6550s driven by a PI I can't remember, and put out 95 watts at clipping (around 1% THD).

[kheper]

t's not that the 8417 put out more power (a pair of 6550s can do 100 watts), it's that the transconductance of the 8417 was so stinkin' high (23,000 µmhos), it took practically nothing to drive them to full output.

That is sorta what I meant. Kt88s are
paralleled to bring these 8417 amps up to
near their original power output specs.

http://www.triodeel.com/8417.htm

[burnedfingers]

These look like they are somewhat interchangeable.

The KT88 or 6550 can be used in place of the 8417 in Quicksilver 8417 mono block amplifiers as well as other amplifiers.

I have sucessfully used KT88,KT90's and 6550 is Quicksilver mono block amplifiers with only a slight bias circuit tweek.

I have used and am currently using some KT88's in a pair of 8417 mono block amplifiers without ANY change to the front end. The amplifiers do not have any problems putting out their rated power with no change in distortion levels.

[burnedfingers]

I ran across this old thread while looking for something else but I thought I would comment on it again.

First of all there is no need to parallel a pair of KT88's to come up with the same power.

Been there and done it so...

A pair of KT88's in a 8417 amplifier will produce a hair over 55watts. You will need to modify the bias circuit to obtain the correct bias for the KT88's.

I currently have a pair of 8417's running 6550's and again modify the bias circuit. Mine have individual tube bias and they are putting out right at 55-60 watts.

Your absolutely not going to be able to tell the difference between 55 and 60 watts.

All of this was done without paralleling the front end. No need to parallel up either the 12AX7 or the 12bh7 in order to run something other than a 8417.

For the record I'm on my 7th or 8th set of 8417 amps.

They will also run 6BG6GA's providing you have the adapters.

[kheper]

First of all there is no need to parallel a pair of KT88's to come up with the same power.

Been there and done it so...

A pair of KT88's in a 8417 amplifier will produce a hair over 55watts. You will need to modify the bias circuit to obtain the correct bias for the KT88's.

I currently have a pair of 8417's running 6550's and again modify the bias circuit. Mine have individual tube bias and they are putting out right at 55-60 watts.

Your absolutely not going to be able to tell the difference between 55 and 60 watts.

The thread was started by asking whether 8417s and 6550s were "interchangeable". See the link below. Some mods are needed on Quick Silver and Bogen amps to run KT88s and 6550s in them. 6550s and KT88s can do 100W, but it stresses them. To run those 8417 designed amps at their specs without taxing the former tubes too hard, a solution is to parallel them. My original response was a bit daft and unclear.

http://www.triodeel.com/8417.htm

[Blair]

Wow!!

Dug straight out of the grave! Believe it or not, just this year, I actually pursued this venture and got a few MO-200s. It has turned into a slightly different beast though. Here is one channel laid out:



It is on hold until after the holidays. I plan on strapping the output iron together in parallel for 2.25k and 200W output capability out of a single PPP 6550 vs. two essentially identical amps with their outputs tied together. (Bridged). I'm still a bit timid to put 680V on the plates, but "no guts, no glory" right?

Blair

[burnedfingers]

With respect to the article on the Quicksilver 8417 modifications. They are totally unnecessary. The front end of the Quicksilver is capable of supplying enough clean signal to get roughly 55 or so watts output. As I noted the bias supply must be modified in order to bias up other tubes correctly.

I have owned a number of sets of the KT88 model as well as the 8417 model Quicksilver amplifier and my actual experience with them indicates the so called mod needed of paralleling the front end is not needed at all.

My suggestion is to rely on actual experience and possible less on what is generally published as the cure all .

With respect to the MO200 amplifier and MO 100 model Bogan. They are run at the extreme end of what generally is considered to be a normal operating region. They run the plate voltage high and the bias high also and this is why they are an accident waiting to happen. As a commercial amplifier they suffer from reliability problems simply because of the design. On the other hand they kick some butt and have an awsome low end.

Yes, you would have to run any other tube hard to come up with the same power that a Bogan 100 or 200 can supply.

[kheper]

First of all there is no need to parallel a pair of KT88's to come up with the same power.

Been there and done it so...

A pair of KT88's in a 8417 amplifier will produce a hair over 55watts. You will need to modify the bias circuit to obtain the correct bias for the KT88's.

I currently have a pair of 8417's running 6550's and again modify the bias circuit. Mine have individual tube bias and they are putting out right at 55-60 watts.

Your absolutely not going to be able to tell the difference between 55 and 60 watts.

The thread was started by asking whether 8417s and 6550s were "interchangeable". See the link below. Some mods are needed on Quick Silver and Bogen amps to run KT88s and 6550s in them. 6550s and KT88s can do 100W, but it stresses them. To run those 8417 designed amps at their specs without taxing the former tubes too hard, a solution is to parallel them. My original response was a bit daft and unclear.

http://www.triodeel.com/8417.htm

I'll have to disagree with the link above. Since I have owned a number of pairs of them and have surely done the measurements I will cry BS to having to parallel the front end.

Once again, I did not say anything about paralleling the front end in this amp. It has been recommended that paralleling 6550 and KT88 tubes for 100W operation in some 8417 amps (not the QS amp), so as not to stress the tubes.

The link is their suggestion and my experience has proven it is unnecessary. As built with the exception of a slight bias modification the "Stock 8417" will come within a few watts of the 60 watt specification the 8417's have.

Well, if bias mods are needed to run 6550s and KT88s in them, then mods are needed, i.e. they are not interchangeable, as part of the link explains.

Quicksilver maintains: "The 8417 tube was one of the last tubes to be developed and is quite different than most other tubes on the market. There is no tube that can be directly plugged in to replace these."

What is your actual experience with them? Owned any? Worked on any? I don't think so

Ad hominem attack.

[Sal Brisindi]

I picked up a pair of Dynaco Mark VI's without the 8417's. Since the 8417's are no longer manufactured, I opted to purchase NOS 8417... 16 of them. A little expensive but I didn't want to modify my near mint Mark VI's..

The seller did test them in front of me with 6550's on a variac. Not at full volume though...

Sal

[Blair]

When I posted this, 5 years ago:), I was unaware of the scarcity of the 8417 which is why it came off so casual.

In the end, even a project that is as expensive as this one has been, I am not interested in the 8417 due to cost and availability.

The datasheet of both the 6550 and KT88 show 100W into 4.5-5K with 300V on the screens. Mr. Bogen ran them easy at 50W/pr which is easily accomplished with the 6550/KT88 and probably the EL34.

In the end, paralleled output transformers leave me with 2.25K, so I'm going with 6550/KT88s unless I talk myself into tapping another pair of holes and go with 6 X EL34s per mono.

I never figured years later, there would be an argument over these tubes;)

Thanks for the resurection and information though!

Blair