[kenm]

This forum has been a big help with building the Hagerman kits - thanks alot to you all! I've recently finished a Cornet but I have a few concerns. Detail and imaging are very good but I find the bass too soft. I was previously using a Bugle and was more then happy with the bass detail and weight. The Cornet has about 50 hours on it and I've already tried a variety of valves including a 5ar4 (currently Bendix 6106, Sovtek 12ax lps and tungsram 12au7.) Resistors are all Kiwame and capcitors are Obbligato.  I adjusted H+ to 6.2 the other night but I hav'nt noticed an improvement in bass weight, rather more detail. Generally voltages are a bit lower than spec but within 10%, I'm running on 230volts and the Cornet is wired for 240 so this is probably why. Any ideas on what else I can try ?
Here's a few pics

[tubesforever]

Interesting,  I am not sure why your Cornet has lower bass response.  I think the Obbligatos are tin foil.  Perhaps the Obbligatos are strangling the bass response?

Do you feel comfortable getting right to tweaks after only 50 hours? 

You might want to give it another 100 hours or so just in case.

In my experience, the incoming signal cap is super critical.  I have tried Panasonic film caps, Auricaps, Dynamicaps, Sprague Vitamin Q PIO caps, Russian K40Y9 PIO caps, and have settled on the Russian teflon FT-3 0.10uf 600 v caps.

I just bought a bunch of the FT-2 0.10uf 200v caps and I think you would find these to be a better fit in your case if you want to evaluate some teflons.  They are clear as a bell with excellent bass response.   

The Auricaps, Dynamicaps and Sonicap version Cornets I have built or heard offer superb bass response.  These caps are all around 20 dollars US.  Only the incoming signal cap and the outgoing signal cap seem to filter the sound quality to do things like you are describing. 

For ultimate bass, I really enjoy the Mundorf silver in oil caps in the final signal output position (C208).  Dang these things really get percussion right.  The Mundorf SIO caps offer excellent bass extension and midrange detail.  The slam is intoxicating!

In terms of gain tubes, the Chinese have some 12AX7 and 12AX7B tubes that are full and rich on the bass lines.  I have a set of Golden Dragon tubes I have owned for years in mine right now.   They are very high gain as well!

My Mullards sound particularly nice in the bass and midrange.  The Groove Tube Mullard style 12AX7 is a very decent tube and I think either the Shuguang or Groove Tubes might be a good place to start.   Pat OMalley likes his Tung Sol tubes so that might be another one to try. 

JJ has some cool taller 12AU7 tubes out now.  They sound as decent as my tall Mullard 12AU7 tubes with a little better top end.  Try a tall JJ when you get the chance. 

Also, the Bugle Boy Amperex 12AU7 sounds mighty tasty as well.

Best of luck. 

[WGH]

I would start with the most affordable option first, try a RCA 5V4GA rectifier.

The Mundorf SIO's are simply the best, I bypassed mine with a pair of Russian teflon FT-3 0.10uf caps resulting in greater clarity and detail without any brightness.

I used Sonicap Gen1's at C202 and Sonicap Platinum at C203.

The Cornet2 is capable of great natural sounding bass once you get the formula right for your room and speakers.

By the way, I used a Hagtech FryKleaner with a iRIAA to put hundreds of hours of burn-in time on these boutique caps without having to spin disks.

[PatOMalley]

The Bendix is good for bass weight but two others which provide a little more is the National 5AR4 and CBS-Hytron Industrial 5Y3WGTB. The CBS being the one I prefer. The CBS adds overall weight to the sound. Both are indirectly heated.

I use the Bendix now in my Clarinet behind RCA command tubes which seem to balance well together.

The National is a Japanese made tube manufactured on Mullard equipment left behind by the company. The Japanese seem to have been faithful to the process.

[wdi]

Regarding the alternative rectifiers.....are these plug and play or do they require resistor changes?

Kenm, cool chassis, but I would get rid of that sticker on the transformer, or at least move it to the underneath side of the chassis.

[amandarae]

Hello,

I am only speaking for myself.  Assuming that you are settled to what rectifier suit your taste, have you tried a different 12AU7 tube?  Have you tried a 6189 tube?

Tubes with high Heater-to-Cathode (Vkh) rating performs best in a CF circuit if I recall correctly.  Vkh is the forward breakdown voltage.  Since my tube manuals does not list Vkh, I assume that a tube that has a  higher Plate voltage, Plate Dissipation, and Plate current rating should also have a better Vkh rating than one with less.  As an analogy, the 6SN7GTB will have better drive in a CF circuit compared to 6SN7, VT-231, or 6SN7GTA because its Plate voltage, Plate dissipation, and plate current is higher than the VT-231, GT, GTA counterparts.

Having said all that, the 6189 have higher ratings of the three parameters compared to a regular 12AU7 tube.  So, you might want to try a 6189 in your preamp and see for the results.

regards,

Abe

[tubesforever]

Kenem,

One other thing I failed to mention is that when I first modified my Cornet 2 i decided to use some polystyrene caps.  I had the values wrong, so when I played music it was bass heavy midbass and midrange heavy the the highs were missing in action.

If your RIAA caps are wrong values then this might also explain you lack of bass response. 

The RIAA calls for 2 each of 0.047uf, and 2 each of 0.001uf values.  if you need more bass response I think a lower value for the  0.047uf might be required.  Perhaps 0.035 might be potentially available.

[kenm]

Thanks for your suggestions. The best way to describe the bass is that it sounds like it's way off in the background. It's deep and tight but hidden in the mix. I also noticed than when I changed to the 6106 rectifier I began hearing some vocal sibilance. I'll try to be patient and run up some more hours on the Cornet. Could just require more break in time. However I will check the .047 and .001 caps to make sure I hav'nt switched positions, and while I've got the bottom off I'll double check all the resisitors as well. I get the feeling it's could be an equalisation issue as Tubes mentions. My setup includes a stepped attenuator feeding a modified T amp, and I read in another post that impedance matching could cause the bass to lose weight. I tried using my headphone amp as a preamp a while ago and got soem good results so I've decided that the next project will be a passive preamp - a PASS B1 to be exact.
In the meantime I'm going to stick with the valves I've got. I've tried some TungSol AX7's but the Sovtek XLPS give more detail.   

[amandarae]

Thanks for your suggestions. The best way to describe the bass is that it sounds like it's way off in the background. It's deep and tight but hidden in the mix. I also noticed than when I changed to the 6106 rectifier I began hearing some vocal sibilance. I'll try to be patient and run up some more hours on the Cornet. Could just require more break in time. However I will check the .047 and .001 caps to make sure I hav'nt switched positions, and while I've got the bottom off I'll double check all the resisitors as well. I get the feeling it's could be an equalisation issue as Tubes mentions. My setup includes a stepped attenuator feeding a modified T amp, and I read in another post that impedance matching could cause the bass to lose weight. I tried using my headphone amp as a preamp a while ago and got soem good results so I've decided that the next project will be a passive preamp - a PASS B1 to be exact.
In the meantime I'm going to stick with the valves I've got. I've tried some TungSol AX7's but the Sovtek XLPS give more detail.   

What about coupling caps?  It's best to check them too.  If it is equalisation issue, the highs will be so pronounce if the bass is weak (from de-emphasis)?

[BobM]

Don't forget to measure around that big sand cast resistor. I found that the stated value in the build may not produce the correct values. This will affect the bass in a big way. I had to add another resistor in parallel to get the measured value to where it should be.

I think this was documented in other threads, so do a search and you should find more info on it.

Good luck,
Bob

[tubesforever]

KenM,

Can you send me your mailing address to jim_howard_pdx@yahoo.com.  I have an emergency triage kit ready to mail out to you.

We will revive the bass lines. 

Cheers!