Guide to buying tube amps

[fronobulax]

Here. Any comments about the article/advice? I was especially interested in the way specific tubes shaped the tone.

 

[capnjuan]

He hit the tops of the tube-tone waves without nuancing the subject to death. When Mr. Schroeder talked about pcb construction, I couldn't help but think of member jazzdj's struggles with his amp. Ok, his problem was in the speaker relays but it could just have easily been in the electronic reverb or chorus ... the disappointment and frustration wouldn't have been any different.

 

[AlohaJoe]

Here. I was especially interested in the way specific tubes shaped the tone.

Yes, I found that info valuable too. Thanks for posting!
- Joe W.

 

[capnjuan]

Hi Frono; the odd-man out of that group is the EL34. It's still being used in Marshall designs but with [expensive] 'ultra-linear' output transformers, the EL34 achieved fame in the 1960s powering two of the best known US-made stereo hi-fi amps; David Hafler's Dynaco ST70 (over 350,000 sold either factory-built or as kits):

... and the Marantz 8b amplifier; in good condition, untouchable for under $3,500 - $4,000:

One of the few US-made EL34-based guitar amps is the Epiphone EA-22RVT 'Mighty-Mite' 50w combo with tremolo and reverb. One of our members owns one:

 

[hideglue]

Good article.

And nice amps, capn!

Of course I'm partial to a quad of KT88s...

 

[capnjuan]

... and understandably so. (some techno-jabber on your favorite valve here) KT88 amp porn: a very fine Mac with a lineup of RI Gold Lions (interesting de-coupling feet ... I think the owner might need to attend Stereophiles Anonymous meetings :wink: )

 

[hideglue]

...(interesting de-coupling feet ... I think the owner might need to attend Stereophiles Anonymous meetings :wink: )

Undoubtedly. Everyone knows that 3 quarters and a penny (wheat penny) stacked at each corner result in a far more blooming soundstage.

 

[Default]

...(interesting de-coupling feet ... I think the owner might need to attend Stereophiles Anonymous meetings :wink: )

Undoubtedly. Everyone knows that 3 quarters and a penny (wheat penny) stacked at each corner result in a far more blooming soundstage.

But they have to be prior to the addition of copper to the quarters, otherwise the midrange is more strident...

 

[mad dog]

I think that is a useful little article. It can only skim the top of some deep subjects. Different tube tones is one such. I've found plenty of differences between the tube types, but overall it's the circuit - the entire amp design - that seems more critical in shaping tone. The more dramatic differences are between amp circuits and/or speaker formats, though tones definitely change as you try different tubes.

My longtime preference has been 6L6, followed closely by 6v6. There is something quite magical about 4 6v6s, same goes for 4 EL84s. If I only get two, I'll take 6v6. Can't get along with EL34. Just got to try some 6550s in a Kingsley D30C, would really like to spend more time with it.

Same tubes, different preamp and/or tonestack, there's another great discussion.
MD

 

[Default]

It's a nice little article, but as you point out Mike, there are a lot of factors that go into a tube amp. I lent my Univox to to one of the assistant pastors at church. He a/bed it with his Pro Junior and liked the dirty tone better. He said that he did not like the clean tone as much as the Fender. A lot of times, you need to find the sweet spot for the right amount of grit.

 

[capnjuan]

Undoubtedly. Everyone knows that 3 quarters and a penny (wheat penny) stacked at each corner result in a far more blooming soundstage.

But they have to be prior to the addition of copper to the quarters, otherwise the midrange is more strident...

... and the silibants become overly enhanced although among the cognoscenti it's pretty well-decided that turning on a light in the next room will help suppress them.

 

[hideglue]

... and understandably so. (some techno-jabber on your favorite valve here)

Dang! I had no idea the market for KT88s was so ripe for forgery. I think I have genuine Golden Lions...

 

[capnjuan]

... and understandably so. (some techno-jabber on your favorite valve here)

Dang! I had no idea the market for KT88s was so ripe for forgery. I think I have genuine Golden Lions...

No wonder your amp sounds so good.

No; nothing's sacred anymore ... btw ... I have 387 Rolexes if you're interested.

 

[capnjuan]

... but overall it's the circuit - the entire amp design - that seems more critical in shaping tone ... My longtime preference has been 6L6, followed closely by 6v6 ...

If I could only have one tube, it'd be a 6V6. If I could only have two, it'd be 6V6s but that's more a function of my interest in time-traveling to recreate the trashy, semi-amateur sound of live music at jHS dances.

LTGer Valcotone, in an effort to understand mysteries of the 5879 as a preamp tube, built a two-channel / 6V6 amp with a 12AX7 in one channel and a 5879 in the other. As he reported here, he didn't get anything like the hot, smoky thing that an old GA40 generates concluding that a lot of it had to do with the cheesy original Gibson parts; murky chocolate-drop capacitors and - by now - somewhat out-of-tolerance carbon composition resistors.

So; if you're making a list of all the things that contribute to tone quality, at least when it comes to older amps, passive components has to go on the list with circuit design, speakers, tone stacks, tube types and everything else.

 

[adorshki]

cheeeez....you guys could probably teach surfers a thing or two about carving waveforms...

 

[Jeff Haddad]

Is that penny heads or tails?

Cap'n - those are some nice stereo amps! Gut shots? I've got a Fisher tube stereo waiting for project time. Don't recall the model, it's 2xEL84/ch.

 

[capnjuan]

Is that penny heads or tails? Cap'n - those are some nice stereo amps! Gut shots? I've got a Fisher tube stereo waiting for project time. Don't recall the model, it's 2xEL84/ch.

Hi Jeff; you'd have to ask hideglue about the coin orientation. Although I've been a member of Stereophiles Anonymous for almost 20 years now, I seem to recall something about tails-up correcting time alignment [we all know how bad that can be] as well as enhancing detail, clarity and imaging ... hahahahaha

No, no gutshots; those are not my amps ... I just never lost my taste for stereo porn. At one time in my obsession, I did have a pair of stock Dynaco ST70s. With bridgeable inputs and by strapping the output transformers, you could get 70 watts/channel of David Hafler EL34 stereo bliss.

Your Fisher is probably EL84s ... tidy space-saving 9-pin packages and don't need a lot of power / big transformers to get nice tone. Below a pic of what a lot of people think of as the flagship of the Fisher product line; the 500C with its 4X7591s. In good condition, they bring big money on eBay:

Does your Fisher have a cabinet? How about the manual and schematic?

 

[Jeff Haddad]

It came with a metal cabinet. Look like Hammond xformers. I don't have paperwork - it was given to me by a guy who I've bought a bunch of guitar amps from - frequent buyer perk, I guess! There weren't any tubes with it, but he gave me a new quad of JJ's. It's missing knobs, but I found pics somewhere and it should have knobs that look similar to marshall amp knobs except the pot shafts are d-shaped IIRC. Not a receiver like the one you posted, it's an integrated amp. I don't remember the model number (on second thought, it could even be an HH Scott? - it's buried way back in the amp closet.)

 

[capnjuan]

... it's an integrated amp. I don't remember the model number (on second thought, it could even be an HH Scott?

Could be; Fisher, Scott, and HK were competing back in the day with decent integrated amps and receivers before the rice-burners. My lo-fi / hi-fi system c. late 80s below; Dynaco PAS-3, FM-3 tuner, and a pair of mid-60s Harmon-Kardon HK250s / 4X7591s with strapped outputs cranking out 50 wpc of quirky mysterious tube goodness tied to a pair of ARC 3xs (?):

My obsession worsened and HKs gave way to the ST70s and a pair of bi-wired Vandersteen 2Cis like these that I still have:

And then an audio comet appeared in the sky; a client - who at the time was the sound contractor for the National Symphony Orchestra and service/maintenance contractor for the sound system at the Kennedy center - needed help but didn't have any cash. He'd put himself through HS and college buying/repairing/selling HH Scott, HK, Fisher-grade stuff and he still had a Marantz 7C and 10b ... both in mint condition and with walnut cabinets; I got them as a retainer. Stock web pics:

I sold the ST70s and replaced them with one of these; a 75 wpc AR D-76a .... 4X6550s w/ a 5th 6550 as a screen voltage regulator:

At that point, the system included the 7C and 10b, a hot-rodded Magnavox 14-bit cd player, a boutique PS audio 2C plus amp feeding the bass speakers in the Vandys the mid-range/highs from AR-D76 via the speakers' built-in crossover ... I was in mid-fi tone heaven and hopelessly obsessed ... which I cured by getting something else to obsess about.

Years ago, Peterson used to publish Audio Amateur. Now gone; reprints only from the linked site. Among the many articles were articles I used to tinker with my stuff:

Audio Amateur 1988 "POOGE-4: Philips/Magnavox CD Mods, Pt 1-2"; I modded my single-shot Magnavox by adding ccomputer-grade polypropylene caps to the legs of the DAC and boosted the uf in the power supply caps after which it ran circles around the next generation of CD players.

Audio Amateur 1981 "POOGE-1: Marantz 7C Mods"; my 7C got a regulated power supply, new Consolidated Electronics non-inductive, wirewound plate resistors ($4/ea :shock: ), a silver-plated ground bus, and a stupidly expensive Alps volume control.

Audio Amateur 1980 "Upgrading FM Tuners"; my Dynaco FM-3 got a solid state power supply and new White Wondercaps ... the Auricaps, Jupiters, SoZos of the era and produced a brooding, delightful tone.

You're probably going to have to find an old fart to work on your amp; people under 40, unless they are tube-obsessed, will have grown up on pcb technology and struggle with point-to-point. They'll also need a schematic but unless something's really torched, all it'll need are a new cord, power supply caps, clean controls ... and, above all, good speakers.

If you make the move, have the tech tie the tape input jacks together; run short wires from the hot and ground posts to the other jack. Get a 1/4"-to-RCA adapter, plug your guitar into the tape input bypassing the preamp ... you can't go wrong. You can take some 000 steel wool to the metal cover and spray it matte black ... (black is known to enhance mid-range tone) and it looks good with the heaters twinkling underneath ... and don't forget to isolate it ... pennies will work just fine ... :wink:

 

[hideglue]

My obsession worsened and HKs gave way to the ST70s and a pair of bi-wired Vandersteen 2Cis like these that I still have:

I remember drooling over the Vandersteens!
And the inspiration for the purchase of the Alon 1s (center) years later... before my neurosis led me to electrostatics.

(web photo)