Can I use 6bq5's in Fisher 7591 amp?

[shacky]

I have a very nice Fisher console tube amp running 7591. I'm borrowing an Eico HF-81 running 6bq5's and loving it

Was wondering if 6bq5's are doable in place of my 7591's. Sorry for the newbe question. I have no idea if they are the same pin design.

 

[markn2wae]

Found this link.

Shacky,

I found this link for converters that convert 7591 to another tube type, maybe just what you need at least for testing.:scratch2:

Look at the last paragraph in the yellow field.

Mark T.

 

[Thespeakerdude8]

In short, no.

The 7591 is more like a 6L6G power and ratings wise. 7591has a plate dissipation of 19 watts, while the 6bq5 only is 12.

The pinout is totally different, the 6bq5 being a B9A nine pin minature socket, and the 7591 being 8 pin octal.

Adaptors will work but the amplifier will have very decreased power output and the plate voltage in the amplifier may very well melt a 6bq5. 7591's will handle up to 500v on the plate.

If you need new 7591's, JJ makes a new one and I think electroharmonix does as well. The new JJ's apparently need the grid resistor changed to a lower value on most amps. Hope this helps!:thmbsp:

 

[Freo-1]

In short, no.

The 7591 is more like a 6L6G power and ratings wise. 7591has a plate dissipation of 19 watts, while the 6bq5 only is 12.

The pinout is totally different, the 6bq5 being a B9A nine pin minature socket, and the 7591 being 8 pin octal.

Adaptors will work but the amplifier will have very decreased power output and the plate voltage in the amplifier may very well melt a 6bq5. 7591's will handle up to 500v on the plate.

If you need new 7591's, JJ makes a new one and I think electroharmonix does as well. The new JJ's apparently need the grid resistor changed to a lower value on most amps. Hope this helps!:thmbsp:

What he said.

The JJ's, in a word, suck. I'd stay away from them.

The EH's get better reviews, and if you get them from Jim McShane, he will stand by them.

Personally, I would spring the money and get NOS from a reputable dealer. The 7591 is a real sweetheart of a tube, easily one of the best I've heard. It's a rare combination of sufficient power for most applications, and yet provides the magic and detail that the low power amps are noted for.

 

[sloober]

Stay clear of the JJ tubes. The 7591EH tubes are the ones you want. My need to change the grid resistors on any new 7591 tubes. While those adapters may work. I doubt you want tubes to be 3-4 inches taller. John

 

[shacky]

Thanks for the quick replies. I saw the Yellow Jacket Sleeve adaptors. You need some serious air space.

The 7591's I have a fine. It's a mix set but fairly closely matched.

I've been using my Sansui 9090DB as preamp. The Sui/Fisher combo isn't as sweet sounding as the Eico. But then again this Eico was gone through by Sam Kim so it's very, very nice.

I think what I'm finding is a need a better preamp to gow with the Fisher iron. Or I need more money to be able to afford a nicely restored Eico

These 6bq5 tubes are wonderful. Amazing bass. Not that the 7591's in the Fisher are shabby. Wish the Eico had a pre out so I could hear how much is its pre amp and how much is the 6bq5.

 

[Freo-1]

Stay clear of the JJ tubes. The 7591EH tubes are the ones you want. My need to change the grid resistors on any new 7591 tubes. While those adapters may work. I doubt you want tubes to be 3-4 inches taller. John

If funds are the primary driver, then the EH gets the nod.

I still think the NOS tube is a better overall performer, and will withstand more abuse, as well as last longer. My buddy (who is a well known tech around here) has worked on a lot of Fisher and Scott units over the years, and he is not a big fan of the EH 7591 tubes.

 

[Freo-1]

Thanks for the quick replies. I saw the Yellow Jacket Sleeve adaptors. You need some serious air space.

The 7591's I have a fine. It's a mix set but fairly closely matched.

I've been using my Sansui 9090DB as preamp. The Sui/Fisher combo isn't as sweet sounding as the Eico. But then again this Eico was gone through by Sam Kim so it's very, very nice.

I think what I'm finding is a need a better preamp to gow with the Fisher iron. Or I need more money to be able to afford a nicely restored Eico

These 6bq5 tubes are wonderful. Amazing bass. Not that the 7591's in the Fisher are shabby. Wish the Eico had a pre out so I could hear how much is its pre amp and how much is the 6bq5.

You are on to something with the better preamp.

I've got a Fisher KX-200 integrated, which has a 12AX7 preamp input. With the Telefunken smooth plates, the overall sound of the Fisher with the 12AX7/7591 is one of the most musical systems I've ever herd (and I've herd a LOT of gear over the years).

I'm sure that's why the Fisher 500 and 800 get so much great ink.

 

[shacky]

Any suggestions for a good preamp to match my Fisher amp? I'm also very impressed with phono section on this Eico.

Only problem is I can hear my refrigerator pulse - when music is not playing with the Eico. Dedeicated line would be nice solution.

 

[Freo-1]

Any suggestions for a good preamp to match my Fisher amp? I'm also very impressed with phono section on this Eico.

Only problem is I can hear my refrigerator pulse - when music is not playing with the Eico. Dedeicated line would be nice solution.

Harmon Karkon Citation IV:

It's simpler than the Citation I, with much the same sound.

 

[rl1856]

No, not without substantial modification.

You can convert the amp to run EL-34 however. The amp was designed to supply power to the companion Tuner-Pre, thus the power supply is robust enough to supply the additional voltage and current needed for the the EL-34. Only ~25wpc, but Wow it sounds great.

Looking back, I should have left the amp stock, if only to gain experience with the 7591 basic amp.

Good Luck,

Ross

 

[kvflyer]

Since you are not in a bind for tubes right now, my suggestion, for what it is worth, is lurk on eBay and make a careful selection of some NOS 7591 tubes. No problem with mixing 7591 and 7591A. Either one will work. While I am not disagreeing with comments above, trust me, I have lots of HH Scott, "There ain't no substitute for vintage USA made 7591 tubes".

Going any kind of substitution route is asking for headache. The little 7591 is quite a powerhouse in a tiny envelope. Amazing!

Just my 2¢...

 

[kvflyer]

And, if you don't mind "coin base" tubes, they come up often and since they are not original looking, they will sell for a lot less than the original base style. And, often used tubes, if the seller will guarantee that they are good, not AS-IS are a good buy, especially if they are not labeled Scott or Fisher, or McIntosh etc...

 

[JonL]

I've used the yellow jackets in my guitar amp... really interesting to be able to change the tone and power of the output stage so easily. I think they were really designed for guitar amps, and would not be very good for hi-fi... the operating point of the tube can't be optimized for every possible circuit with one adapter device.

 

[shacky]

Since you are not in a bind for tubes right now, my suggestion, for what it is worth, is lurk on eBay and make a careful selection of some NOS 7591 tubes. No problem with mixing 7591 and 7591A. Either one will work. While I am not disagreeing with comments above, trust me, I have lots of HH Scott, "There ain't no substitute for vintage USA made 7591 tubes".

Going any kind of substitution route is asking for headache. The little 7591 is quite a powerhouse in a tiny envelope. Amazing!

Just my 2¢...

Well I put my Fisher 7591 back in rotation. Great sounding. And can drive my KLH's much better than the 6bq5 Eico. Those JBL L36 get a little fatiguing to me. I'm more comfortable listening to the KLH.
Running the Sui 9090DB as preamp again. Noticed I had a little static in my Dolby pot. Probably need to reflow the solder joints on that Dolby board.

 

[Freo-1]

Since you are not in a bind for tubes right now, my suggestion, for what it is worth, is lurk on eBay and make a careful selection of some NOS 7591 tubes. No problem with mixing 7591 and 7591A. Either one will work. While I am not disagreeing with comments above, trust me, I have lots of HH Scott, "There ain't no substitute for vintage USA made 7591 tubes".

Going any kind of substitution route is asking for headache. The little 7591 is quite a powerhouse in a tiny envelope. Amazing!

Just my 2¢...

What he said...

I am in 100% agreement. You simply cannot beat the NOS American 7591 tube. It's a great little power tube, easily one of the most musical I've heard. It also has enough power to drive most speakers to acceptable levels.