Tone advice for high frequencies: do I need new tubes?

[theWalrus]

Hello good people, it's been a while; how are you doing?

I still have that '69 Hiwatt DR103 but I got a new Marshall 1959HW Super Lead 100W head this summer. And by comparison, I figured out a tone issue:

I was playing a song with bends on the 22nd fret high E string, and I could barely hear any sound from the Hiwatt there. A few frets up, and it's several dB's lounder; better said, screechingly louder.

So I thought: maybe my hearing is already pretty bad (not impossible!) or there is an intonation issue with the guitar. Thing is: I just got the guitar back from my tech specifically for intonation improvement, and it is spot on; you can tell even acoustically. So, I tried the same pedals in front of the Marshall (at the same settings and same cab) and... I get that 22nd fret to sing and there isn't much of a volume difference perceived as I go to other frets; they are all equally loud. I ran both amps with all settings (except for volume) maxed out to guarantee it's not a presence knob or EQ issue. The actual volume after attenuation in both was also about the same (~105 dB).

So, here is my guess: I need new, better tubes, and an amp tech visit. The tubes I'm using are from Mesa Boogie; they are from the last owner. I've heard great things of Mullards. Could anybody help me pinpoint the best tube model? I'm assuming a Mullard EL34 reissue is a good choice for great blues-rock. The other tubes I had in mind are KT66 (as used in the JTM45/100) but I don't know the best manufacturer, if they happen to vary.

Please don't grill me for the Marshall. I still love my Hiwatt.

Many thanks

[OldSchoolDave]

First of all, KT66's are not going to be a direct substitute for EL34's. You'd have to make bias adjustments and then would be taking away some of what makes a vintage Hiwatt a vintage Hiwatt...

Secondly, whenever I hear of a note dying away on a pull, I think of a high fret getting in the way. Your results on the other amp still seem to indicate there's some loss of resonance, if I'm reading correctly.

It's possible something in your Hiwatt is harmonically challenging that particular note, but would look into preamp tubes before power.

There are plenty of discussions of tubes - both pre and power - on the forum. Search around and you'll find some perennial favorites.

Good luck in resolving the issue,
Dave

[theWalrus]

Thanks for the advice. Based on what you recommended, seems like it would be a good idea to order (4) ECC83 preamp tubes. They look like this



But the amp front looks like this:



So I'm assuming those gray cylinders are just preamp tube covers. By the way, here is a picture of the back with the current tubes:



Do you happen to know a good reference on finding vintage Mullards (preamp and power tubes) for the most authentic DR103 sound?

Thanks

[mhuss]

Those Mesa tubes look like 6CA7s, electrically similar but tonally a bit different, similar to KT77s. I'm quite fond of the way these sound in a DR103.

--mark

[Dr.HI-TONE]

that amp is a '73 with at least one modification visible (the fixed power cable through the serial tag)
You may want to post clear pics of the circuitry as it is possible that there are more mods internally that affect the tone.

You would need 3 ecc83/12ax7 and one ecc81/12at7 for the phase inverter.

I tried those new mullards and was tremendously dissapointed. I much prefer JJ's if you use new production tubes.
Those electrolytic caps are the originals and are almost certainly over due to be replaced.

[theWalrus]

Thank you so much for your responses. So, here is the bottom



Is there any obvious mod besides the power supply cable?

Anyhow, Based on your responses for maintenance, I should get these:

- Electrolytic caps. So I can show it to my tech and see if there is need, which of these is meant for a vintage DR103?
http://shop.hi-tone-amps.com/HI-TONE-DR ... 201RCK.htm
http://shop.hi-tone-amps.com/VHR-1616-R ... ap-kit.htm
http://shop.hi-tone-amps.com/VHR-1632-R ... ap-kit.htm
- (3) ecc83/12ax7 preamp tubes
- (1) ecc81/12at7 for the phase inverter.

These pictures may help identify the year a bit easier.

A) Hylight serial # 4533



B) Transformer codes: TG9302/H2093A



illegible/H3058C



I've been itching to try other power tubes also. I still have to educate myself on how to identify period-correct mullard power tubes if they are worth the trouble.

Thank you so much. Have a good weekend.

[Dr.HI-TONE]

can you take a better pic than the overall interior pic? it isn't diagnostic.
I already correctly dated the amp as a 1973.

the 16+32 kit is the best fit for this amp. and it needs recapped.

While I do not like the new mullard 12ax7, I don't hate the new mullard EL34.
I still like the =C= EL34 if you get them burned in and matched. 4-5 years ago, these were hands down the best, in recent years the quality has been a little hit and miss. Thus the recommendation that they are burned in.