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PostPosted: 26 Dec 2012, 17:19 
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Joined: 19 Mar 2012, 19:22
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Location: Wales, UK
I was wondering if there is a way of changing the tonal qualities of an amplifier. The amp is currently using brand new Tungsol 6550 (re-issue). I find that the mid range to be a bit to harsh, bass is solid with a nice top end response but vocals seem to sound to forward. Should I leave the amp as is for now to allow it some time to run in? The Tungsols have at the most around 6 hours on them.

Many Thanks

Phil


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PostPosted: 26 Dec 2012, 21:10 
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Location: Arizona, USA
Hi, First I would put a few more hours on the tubes. They may improve. The only Tungsols I use are the new KT120s and they are actually pretty good from the the start and don't mellow much with use. It may be possible depending on the design of the amp to change the tone to get what you want. In my designs I have found that the coupling capacitors can cause a significant change in the sound. This is easy to do as there is only one capacitor in the signal path in the power amps. A number of brands of capacitors in that location are really unsuitable and sound somewhat like what you are describing.

Ones I like are:

Auricaps, warmish with good overall detail and a nice range top to bottom

Jantzen Siver Z, neutral, very clean sound, IMHO the best in my designs. They tend to be a bit pricey. Do not confuse with the Superior Z, Crosscap and standard Z as they are all lower in perfomance

Russian K40Y-9 paper in oil caps, in many ways nearly as good as the Jantzens, a tad bit warmer (inexpensive, great bang for the buck)

Quality Cap ESA, neutral with a slight bias toward both top and bottom, IMHO similar to the Auricaps just not to my preference, other folks might prefer them over the Auricaps.

Quality Cap MR, better than the ESA, rather nice overall but IMHO not as nice as the Jantzens

Kimbercaps, similar to the Auricaps, but a little less warm

Solen, mostly neutral, not in the same league as the others

Mallory, ditto the Solen

Sprague, ditto again

I have omitted caps that are in the extreme high cost and low cost ranges. IMHO the very high end ones may be better, but the cost gets out of hand quickly, especially if you need several in the amp. The cheap ones are just that, you get what you pay for.

Another thought is that you might consider changing the driver tube(s). They can flavor the sound as well. Many NOS ones are warm and detailed with the new equivalent ones much brighter. This is particularly the case in the 12A_7 families of tubes. Nice thing about tube swaps is you don't need to rewire anything. Ask about particular tubes on the forums, I have found that companies that sell the tubes just parrot what the manufacturer tells them to say and are not particularly accurate.

Good listening
Bruce

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PostPosted: 27 Dec 2012, 00:24 
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philip davies wrote:
I was wondering if there is a way of changing the tonal qualities of an amplifier. The amp is currently using brand new Tungsol 6550 (re-issue). I find that the mid range to be a bit to harsh, bass is solid with a nice top end response but vocals seem to sound to forward. Should I leave the amp as is for now to allow it some time to run in? The Tungsols have at the most around 6 hours on them.

I'm with Bruce here, give the tubes 50 hours at least. Then decide. The preamp I built recently, sounded awful for the first few hours and has just kept getting better. Give the big tubes even 200 hours.

If you used tube rectification you can roll the rec. tube. Inter-stage caps are right in the signal path and caps have a huge influence on sound. So, as Bruce said, consider others. I like to bypass my cathode caps (Ck) with 0.1uf polices for what I believe is better mid and highs.

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PostPosted: 27 Dec 2012, 04:54 
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I'd advice You use interstage caps K40-U9, K42-U9 about 0.47 - 1 uF, IMO they sound better Auricap and Mallory, use big cap cathode shunt about 1000-2000 uF /Black Gate, Elna, Rubycon, Panasonic/ for output and input tubes, for big bass. Don't shunt them small parallel cap, this decrease quality in MF and HF, because signal cross different medias. You can put in PS electr. caps 470-680 uF for big bass, they provide more energy in LF.. And Use in input stage tubes 12AU7, 12AT7, ECC88, PCC88, 5687, audiophill E180F, with more current, decreasing plate and cathode resistor, according line of plate dicipation. At lest use bigger output transformer, with more iron.

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Hi End is back proportional to the number of composite parts!
Projects: OTL 6AS7 Gen, Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, PP 6005 Gen. Ellectric , headphone ampl. OTL Loftin White 6AS7 RCA....SE E84L& E80CC Siemens&Tel-n.
http://azazello-sound.blogspot.com/


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PostPosted: 27 Dec 2012, 06:27 
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Personally I would be careful with too bigger inter-stage and Ck cap.I have been alluded to timing issues which may occure from grid through to Ck.

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PostPosted: 27 Dec 2012, 08:23 
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Joined: 19 Mar 2012, 19:22
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Location: Wales, UK
Thanks everyone for your advice. I forgot to note that the decoupling caps are Mundorf Silver/oil which are also quite new. I've been advised by the seller that they need some time to run in. The cathode bypass caps are Epcos which were cheap but I do have some Elna Cerafine waiting to be installed in my amp. The driver stage uses JJ ecc803s and JJ gz34 for rectification. These valves have many hours on them, probably well passed 150 hours

I think I will put more hours of use on the Tungsols and maybe order some NOS 12ax7 or 5751 for the driver stage and see how it sounds and if it's not quite to my taste then I will try other brands of capacitors.

Many thanks again :D

Phil


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PostPosted: 27 Dec 2012, 09:33 
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I'd advice You don't use 12AX7, it sounds sharp and not comfortable, it is for lead guitar amplifiers.

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Hi End is back proportional to the number of composite parts!
Projects: OTL 6AS7 Gen, Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, PP 6005 Gen. Ellectric , headphone ampl. OTL Loftin White 6AS7 RCA....SE E84L& E80CC Siemens&Tel-n.
http://azazello-sound.blogspot.com/


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PostPosted: 27 Dec 2012, 11:25 
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Joined: 19 Mar 2012, 19:22
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Location: Wales, UK
Hi,

Thanks for that. Should I try the lower gain 5751 or perhaps changing the circuit to suit something else, like the 12au7?

Many Thanks

Phil


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PostPosted: 27 Dec 2012, 16:51 
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Joined: 01 Jun 2012, 09:56
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Fresh output iron also needs a bit of time to stabilize.


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PostPosted: 27 Dec 2012, 17:40 
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azazello wrote:
I'd advice You don't use 12AX7, it sounds sharp and not comfortable, it is for lead guitar amplifiers.

I have found the 12AU7 better sounding but less gain.

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