"The JTM45 is really just a Fender Bassman"

[EdPero]

Everything I red here reminds me the discussions I had with a french guy who makes amps and effets (like amps simulations in pedals). I know one thing about Marshall : the JTM amps are the only ones I like because the clean sound is really clean -not like the horrible clean channel on the JCM after one hour of playing !- and the drive on a JTM is always crispy and warm.

 

I played on a Fender Bassman and the only comparison I can do is about the input level. The JTM can take a high level input (like a Fender Twin) without compressing the sound, which is useful when you use a lot of amps simulation pedals like me. The Bassman is a bit more compressed and your sound sounds less large than on a JTM. Or maybe it was the Bassman I used that was too old for rock n roll... I can't explain that phenomenon with "tubes" or "valves" vocabulary, I'm not good enough in electronics.

[212Mavguy]

Everything I red here reminds me the discussions I had with a french guy who makes amps and effets (like amps simulations in pedals). I know one thing about Marshall : the JTM amps are the only ones I like because the clean sound is really clean -not like the horrible clean channel on the JCM after one hour of playing !- and the drive on a JTM is always crispy and warm.

 

I played on a Fender Bassman and the only comparison I can do is about the input level. The JTM can take a high level input (like a Fender Twin) without compressing the sound, which is useful when you use a lot of amps simulation pedals like me. The Bassman is a bit more compressed and your sound sounds less large than on a JTM. Or maybe it was the Bassman I used that was too old for rock n roll... I can't explain that phenomenon with "tubes" or "valves" vocabulary, I'm not good enough in electronics.

 

I'm right there with you on that one, my Siggy sounds like a Steinway piano the cleans are so detailed and sweet...the basic amp design, the super top end parts and especially the OT are a big part of it, but I have some pretty special vintage old stock tubes in the preamp besides having some rather special British kt's in it. And that special tone quality goes up clear into the 80's kind of rock crunch tones kind of gain. Can't have enough praise for that amp.

[rjsanders]

i've got a Heritage Colonial setup for JTM/Bassman tones (difference is amount of negative feedback, there's a "MOOD" control for that) and a PaulC one-off of a JCM800. the JCM-like thing is just like a Marshall, the diff being Heritage custom transformers. when i got the JCM-like gadget it was way too gainy & bright for me and re-bias helped that significantly. but a re-tube from EL34s to 5881s completely changed everything. now very much like the cleans of a JTM, with the "GAIN" set appropriately.

 

just a sidenote. do original JCM800s take 5881s w/o complaint?

[212Mavguy]

i've got a Heritage Colonial setup for JTM/Bassman tones (difference is amount of negative feedback, there's a "MOOD" control for that) and a PaulC one-off of a JCM800. the JCM-like thing is just like a Marshall, the diff being Heritage custom transformers. when i got the JCM-like gadget it was way too gainy & bright for me and re-bias helped that significantly. but a re-tube from EL34s to 5881s completely changed everything. now very much like the cleans of a JTM, with the "GAIN" set appropriately.

 

just a sidenote. do original JCM800s take 5881s w/o complaint?

 

Original JCM800's? Depends on the plate voltage, whether there is a bias pot and what kind of 5881's...Vintage Tung Sol and Sylvania/Philips 5881 and 6l6WGB types are a ruggedized version of the GB series of 6l6, hence the "W" in the tube numbering. They are rated for lower plate voltage than 6l6GC, which came into being at a later date. My guess is that those tubes might get cooked to an early death in a JCM 800. My Siegmund has the lowest voltage power transformer option from that builder installed. I'd be surprised if the JCM800 did not have plate voltage in the 475-525v range. The older, aforementioned US made 5881 and 6l6WGB should not be run much over 375-400 volts to get to an appropriate bias. El34's draw less current for a particular bias pot setting than 6l6 types, you will want to rebias the amp to use 5881's if it had el34's previously.

 

The Russian 5881's (Sovtek and Panno) are rated for higher plate voltages than the early American ones. I don't know about the Tung Sol Reissue 5881's, my guess is that they will be able to handle the higher 6l6gc type voltages found in modern amps. One trend that is getting going recently in a few boutique amp builders is a swing in the pendulum back towards lower plate voltages overall. If that trend becomes more popular then demand for vintage power tubes will increase, along with prices.

[rjsanders]

yes, the new TS 5881s will handle max 400Vdc (they're reportedly mechanically & spec-wise identical to the oldies). the Heritage amps all come with external bias ports & it's a quick deal to rebias w/a VOM...

 

(i'm no electronic wiz m'se'f, just following instructions)

[212Mavguy]

yes, the new TS 5881s will handle max 400Vdc (they're reportedly mechanically & spec-wise identical to the oldies). the Heritage amps all come with external bias ports & it's a quick deal to rebias w/a VOM...

 

(i'm no electronic wiz m'se'f, just following instructions)

 

Then I would not use the Tung Sol 5881 reissue in a JCM800...and I'd be surprised if the Heritage amps designed for 6l6/el34 aren't higher than 400 plate volts...

[rjsanders]

Then I would not use the Tung Sol 5881 reissue in a JCM800...and I'd be surprised if the Heritage amps designed for 6l6/el34 aren't higher than 400 plate volts...

 

depends on bias values. EL34s are set at 30-40mv, 6L6s at 25-35mv (these are values recommended by PaulC based on the bias circuit). KT66s and 6550s are supportable, too. the Colonial will even support 6V6s, but only with a 5U4 rectifier & never run in the "PUNCH" setting (solid-state recto) - but Paul doesn't think it sounds very good.

 

sidenote: i tried a pair of THD yellow jackets this week. interesting. liked the knock down in output level and the lows and mids. didn't like the very high highs no matter what EQ settings or speakers i tried (too brittle or something), so i put it back on 5881s after a couple days.

[slider313]

Original Tung Sol 5881's, as well as most other power tubes from years ago, were overdesigned. The 400v rating is a "safety net" and like other components of the day the + or - 20% rule applies. I have a 1960 Fender Super running a pair at 455v with no problems. 1961 Fender Concerts ran them upwards of 470v (solid state rectifier) with no problems.

 

Bias current and plate voltage are two different thing; yet both determine a safe operating bias.

[212Mavguy]

Original Tung Sol 5881's, as well as most other power tubes from years ago, were overdesigned. The 400v rating is a "safety net" and like other components of the day the + or - 20% rule applies. I have a 1960 Fender Super running a pair at 455v with no problems. 1961 Fender Concerts ran them upwards of 470v (solid state rectifier) with no problems.

 

Bias current and plate voltage are two different thing; yet both determine a safe operating bias.

 

Yep, I agree on that, and it depends on the brand. For instance, using bendix red bank tubes you really need to stay within operating limits, those limits are the limits, period, especially screen voltage. Users of those in guitar amps can get some wonderful tones but they like really rock solid stable voltages besides staying within their limits. Vintage Tung Sol 5881's and Mullard el38's have some gold in their grid wires, and they were designed as long life tubes.

 

One Mesa Boogie board member who is also a tech ran some vintage TS 5881's in one of his amps, he had installed an adjustable bias mod and they still died pretty quickly. If one chooses to exceed a tube's ratings in all areas simultaneously that tube will die comparatively quickly, any brand.