I've been curious about the new Dr Z DB4 amp which similar to amp I've wanted to build the Brown Note Foxy 18 and the EF86 Marshall.
The New Dr Z DB4 uses the 5879 tube like many of the Hoffman Forum guys have been using and I built one of their amps with that tube myself.
Another project down the road but I did buy some more 5879 tubes to have in stock.
Mark
Something like a DB4 amp
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Something like a DB4 amp
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Re: Something like a DB4 amp
That's going to be a cool project Mark. I like the way that amp sounds.
Re: Something like a DB4 amp
Kind of Voxy first position then goes into Marshall territory right Dave?
Re: Something like a DB4 amp
I wonder how close to DaGeezer's HoSo56 this amp is?
With respect, 10thtx
EDIT: Nevermind, it's obviously different. Looks like a 5879 straight into an LTPI. I do wonder what values they used with 5879.
With respect, 10thtx
EDIT: Nevermind, it's obviously different. Looks like a 5879 straight into an LTPI. I do wonder what values they used with 5879.
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David Root
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Re: Something like a DB4 amp
Current issue of Tonequest magazine has an interview with Dr. Z. where he discusses the DB4 amp.
Without scanning & uploading a couple of pages from the article, which might infringe copyright, I read that Z points out that the 5879 is what Les Paul had Gibson put in the mid-'50s Les Paul GA-40, which is "full frequency with a nice gain structure and is sonically biased at lower mid and rich bass response". He does not say if that is how he biased the DB4 5879, or if that is how Les Paul had the GA-40 5879 biased. In general that statement IMO describes how the 5879 differs from the 12AX7, which is no secret.
In that regard, I'm currently building a 4x6BM8 version of Geezer's famous Little Wing amp, (see the EL34 forum) with a first stage switchable between a 12AY7 in parallel (from the Little Wing) and a relatively low gain (for a pentode) 5879 set up as in the HoSo56 above, as I've used the 5879 with success before, it is a great tube.
Z also said it is "loosely based on the Selmer Zodiac design, an extremely underrated vintage amp which had its own unique voice". Assuming he meant the Zodiac Twin 30, that uses an EF86 in each channel, not a 5879. In each case the EF86 is the recovery stage for a 12AX7 first stage thru a tonestack, which is different topology than the GA-40, where the 5879 is the first stage. The Zodiac channel 2 5879 "drives a rotary switch tone select control" which I think is what Z is talking about with the Zodiac. This appears to be RLC cut controls like a Dumble Steel String Singer uses.
The Tonequest reviewer describes the DB4 as having a thick rich tone that "kills with a Robert Cray Strat".
If you want to delve into this I would suggest looking at the '57 GA-40 and Selmer Zodiac schems, both of which are readily available, and buy the May 2016 Tonequest Report. Tonequest is a great mag, always full of quality stuff for tonefreaks, as it's owned by one!
Without scanning & uploading a couple of pages from the article, which might infringe copyright, I read that Z points out that the 5879 is what Les Paul had Gibson put in the mid-'50s Les Paul GA-40, which is "full frequency with a nice gain structure and is sonically biased at lower mid and rich bass response". He does not say if that is how he biased the DB4 5879, or if that is how Les Paul had the GA-40 5879 biased. In general that statement IMO describes how the 5879 differs from the 12AX7, which is no secret.
In that regard, I'm currently building a 4x6BM8 version of Geezer's famous Little Wing amp, (see the EL34 forum) with a first stage switchable between a 12AY7 in parallel (from the Little Wing) and a relatively low gain (for a pentode) 5879 set up as in the HoSo56 above, as I've used the 5879 with success before, it is a great tube.
Z also said it is "loosely based on the Selmer Zodiac design, an extremely underrated vintage amp which had its own unique voice". Assuming he meant the Zodiac Twin 30, that uses an EF86 in each channel, not a 5879. In each case the EF86 is the recovery stage for a 12AX7 first stage thru a tonestack, which is different topology than the GA-40, where the 5879 is the first stage. The Zodiac channel 2 5879 "drives a rotary switch tone select control" which I think is what Z is talking about with the Zodiac. This appears to be RLC cut controls like a Dumble Steel String Singer uses.
The Tonequest reviewer describes the DB4 as having a thick rich tone that "kills with a Robert Cray Strat".
If you want to delve into this I would suggest looking at the '57 GA-40 and Selmer Zodiac schems, both of which are readily available, and buy the May 2016 Tonequest Report. Tonequest is a great mag, always full of quality stuff for tonefreaks, as it's owned by one!
When I was a boy I was told that anyone could become President. I`m beginning to believe it--Clarence Darrow
Re: Something like a DB4 amp
It would be interesting to see if it is LTPI or paraphase. I've never
seen one of his PP amps without LTPI so I'm taking that for granted.
I have started my GA-40 project with a preamp board, but stalled
out with other projects taking priority.
seen one of his PP amps without LTPI so I'm taking that for granted.
I have started my GA-40 project with a preamp board, but stalled
out with other projects taking priority.
BLT
Re: Something like a DB4 amp
The chassis gut shot that was posted looks like an LTPI to me.It would be interesting to see if it is LTPI or paraphase.
With respect, 10thtx
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Smokebreak
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Re: Something like a DB4 amp
I'm looking forward to seeing what you come up with Mark. I hope you don't mind me adding to your thread here. I was about to do some heaters for a different amp when I saw this thread, and took a quick detour to wire the first socket for 5879, as I've had a couple sitting around for a while 
I should note this amp is wired for octal outputs, and I have 6V6s in there.
I used a board for another amp too, which is why it looks so strange.
Anyways, I built from that gutshot and though I couldn't see some values, looking at the datasheets, and other amps that use that tube, and ears, I got a sweet amp outta the deal.
For the 5879, with a supply voltage of 285, I found these two things work well at the extremes of the spectrum:
- 2K2/25u cathode, 110K plate, 470K screen, .05 cap to ground from screen
That provides a nice clean amp with mildish breakup when cranked. Note that the datasheet would call for a much smaller Rk for the given supply voltage and Rp. Haven't tried that yet...
However, if you reeeealy wanna have some fun(and stick to the sheets), try :
-470K plate, 1M screen, and a 150K paralleled to your screen cap to ground. The 150K keeps the voltages in check, as otherwise my plates dropped from 170V way down to 40V or something, but oddly didn't have THAT much affect on the tone, like it would with a triode. Still trying to figure that out.
Anyways, that arrangement is just like the GA40 trem channel, and sounds like rock and roll when cranked.
Inbetween the first stage and the gain pot is the rotary RC filter, and mine consisted of the .02 Rp, a 1M2 pop resistor to ground, and 3 caps to choose from, that are more or less in series with the Rp: .02, .002, 500p. My rotary is a 4 way, so the top 2 selections are ultimately .02 and .01, which are redundant more or less. I'm gonna change to .002,.001, 500p, then have the stock .02.
I didn't find the small caps useful until I got the amp cranked, and you definitely want the higher cutoff there, at least with the looseness of 6V6s. The amp sounds amazing right there though with SC and HB, and isn't too loud if no one is home
I'm gonna wire up another gain stage and see what happens
I should note this amp is wired for octal outputs, and I have 6V6s in there.I used a board for another amp too, which is why it looks so strange.
Anyways, I built from that gutshot and though I couldn't see some values, looking at the datasheets, and other amps that use that tube, and ears, I got a sweet amp outta the deal.
For the 5879, with a supply voltage of 285, I found these two things work well at the extremes of the spectrum:
- 2K2/25u cathode, 110K plate, 470K screen, .05 cap to ground from screen
That provides a nice clean amp with mildish breakup when cranked. Note that the datasheet would call for a much smaller Rk for the given supply voltage and Rp. Haven't tried that yet...
However, if you reeeealy wanna have some fun(and stick to the sheets), try :
-470K plate, 1M screen, and a 150K paralleled to your screen cap to ground. The 150K keeps the voltages in check, as otherwise my plates dropped from 170V way down to 40V or something, but oddly didn't have THAT much affect on the tone, like it would with a triode. Still trying to figure that out.
Anyways, that arrangement is just like the GA40 trem channel, and sounds like rock and roll when cranked.
Inbetween the first stage and the gain pot is the rotary RC filter, and mine consisted of the .02 Rp, a 1M2 pop resistor to ground, and 3 caps to choose from, that are more or less in series with the Rp: .02, .002, 500p. My rotary is a 4 way, so the top 2 selections are ultimately .02 and .01, which are redundant more or less. I'm gonna change to .002,.001, 500p, then have the stock .02.
I didn't find the small caps useful until I got the amp cranked, and you definitely want the higher cutoff there, at least with the looseness of 6V6s. The amp sounds amazing right there though with SC and HB, and isn't too loud if no one is home
I'm gonna wire up another gain stage and see what happens
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Re: Something like a DB4 amp
Good report thanks for adding your findings and photos. 