• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Olson/Dolly clone SE 6BQ5 build

Popped in a full compliment of EICO branded Mullard tubes and:drool::drool::drool:

If sound could be described as food, it would be a giant vat of melted chocolate. This amp into a pair of Dynaco A25 sounds fantastic!
 

Attachments

  • IMG_0625_800x580.jpg
    IMG_0625_800x580.jpg
    57.4 KB · Views: 15
  • IMG_0628_800x563.jpg
    IMG_0628_800x563.jpg
    39 KB · Views: 13
Surprisingly, yes!

The way the bass blooms and the high end rolls off on the A25s seems to be a great match for this amp.

Though my taste in music is mainly acoustic, vocal jazz, etc. Not too demanding. The Rotel preamp will drive the tubes into "clipping" where the sound breaks up but I can easily get a reasonable volume before this happens.
 
So, I decided to update this old thread after a few years! I really enjoyed this this little Dolly clone amp and put many hours on it - but I was never able to eliminate that pulsing "hum" mentioned in post #22. The thing was a bit "prototype-y" to say the least. It sat in the closet for a few years.

Recently I got the itch for tubes and decided to strip out the amp and start over. The new version is built on the same chassis with the same output transformers set into a MDF base veneered in walnut. The transformers are now enclosed for aesthetics.

The amp circuit is still Redboy's Dolly amp - with a little more thought and experience, on my part, put into the wiring layout. I changed the power transformer and cheated a bit by using a pre-designed power supply board (modified slightly) for the high voltages.

The old Mullards were testing weak so the amp now has new Gold Lion EL84s and a Sovtek 12AX7 for the time being.

It's currently playing through a set of Heresys that are on the list of future projects. Parts are also on the way for a matching preamp using 2 x 12AX7.

IMG_5333.jpeg IMG_5331.jpeg IMG_5332.jpeg IMG_5278.jpeg
 
willyrover said:
So, I decided to update this old thread after a few years! I really enjoyed this this little Dolly clone amp and put many hours on it - but I was never able to eliminate that pulsing "hum" mentioned in post #22. The thing was a bit "prototype-y" to say the least. It sat in the closet for a few years.

Recently I got the itch for tubes and decided to strip out the amp and start over. The new version is built on the same chassis with the same output transformers set into a MDF base veneered in walnut. The transformers are now enclosed for aesthetics.

The amp circuit is still Redboy's Dolly amp - with a little more thought and experience, on my part, put into the wiring layout. I changed the power transformer and cheated a bit by using a pre-designed power supply board (modified slightly) for the high voltages.

The old Mullards were testing weak so the amp now has new Gold Lion EL84s and a Sovtek 12AX7 for the time being.

It's currently playing through a set of Heresys that are on the list of future projects. Parts are also on the way for a matching preamp using 2 x 12AX7.

View attachment 2346513 View attachment 2346514 View attachment 2346515 View attachment 2346516
Click to expand...
Despite its name, this forum seems to have relatively few DIY projects that involve tubes. You'll get more response and expertise over on the Tubes forum. You could start a new thread or click on "Report" and ask the moderators to move the thread, if you'd like.

The pulsing you described sounds like it might be low frequency oscillation, aka "motorboating". Do a search for more info or ask on the Tube forum.

You really don't need an additional preamp to drive your SE 6BQ5 / EL84 amp since it already has a 12AX7 at the input. You'll end up with way too much gain. Great if you're building a guitar amp and want distortion, but not for stereo use.

I inadvertently discovered that it's possible to build a Spud amp with a pair of 6BQ5s. A
Spud, if you're unfamiliar with the term, is an amp with only one tube per channel. So no preamp tube at all, just the pair of 6BQ5s. Here's a thread about it with some pics and the final schematic at the end:

https://www.audiokarma.org/forums/index.php?threads/voice-of-music-se-6bq5-w-local-nfb-build.926391/

And a link to my recent post about it on the thread about flea powered amps, which has all sorts of low powered amps including a few Spuds:

https://www.audiokarma.org/forums/index.php?threads/show-us-your-flea-watts-amps.545147/page-25

Probably the most popular SE 6BQ5 build is discussed in this massive and legendary thread which is based on the little Magnavox 8600, which uses a single input tube (6EU7 or 12AX7, which are electrically the same but have different pinouts) and a pair of 6BQ5s:

https://www.audiokarma.org/forums/i...ore-out-of-the-8600-series-a-lot-more.665735/

Love the look of your amp - super clean!
 
You must log in or register to reply here.
Back
Top Bottom