807 bassman works

[Geezer]

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ernie jr
Junior tube assistant
Posts: 13
(11/7/03 9:55 pm)
 807 bassman works
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 just finished my hoffman style bass with 807's with matching o/p transformer. the amp sounds great up unitl about 4-5 on the volume, then it begins to distort. never palyed a bassman before, so not sure if this is normal or not. only other changes besides the 807's are 47, 40, 22, 22 for the filter caps and and old stancor choke. i have not biased the amp yet, so it may need some tweaking. i am getting about 325 volts off the p/t before the rectifier, -50 volts bias. the rest of the voltages have not yet been measured. i will post when i get them. thanks to all for the help on my questions along the way.
thanks again
ernie
 
ernie jr
Junior tube assistant
Posts: 17
(11/15/03 9:47 am)
 bassman voltages
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 ok here are the voltages, any of them close, thanks to all

pin v1 v2 v3
1 175 185 265
2 0 0 25
3 2.75 1.1 50
6 160 330 250
7 0 185 22
8 2.75 185 50


pin pt1 pt2
1 0 0
3 425 425
4 440 440
5 -48 -48
8 0 0

all filaments are at 6.3 amp works but seems to distort
at volume 5 and above. the amp is very quiet with virtually no hum. the 807 have a nice sound. the o/p trans that i am using has 9000 ohm primary (it was used with the 807's in an old williamson amp. thanks for all the help
ernie
i still need to set the bias current
 
ernie jr
Junior tube assistant
Posts: 23
(11/18/03 8:45 am)
 any help on voltages?
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 any comments on the boltages, thanks
ernie
 
GroundhogKen
Forum Moderator
Posts: 2048
(11/18/03 6:37 pm)
 Re: any help on voltages?
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 The preamp tubes look good.

I'm not familar with 807s. What is their maximum plate dissipation rating? Do you know how much plate current is flowing?

Ken
 
ernie jr
Junior tube assistant
Posts: 24
(11/19/03 7:13 am)
 bassman 807's
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 807's have virtually the same specs as 6l6's.
they are big coke bottle tubes with the plate coming out of the top of the tube. the look real retro. i had 2 matched pairs, which is why i used them.
thanks for the info
how do i measure the plate current?
ernie
 
GroundhogKen
Forum Moderator
Posts: 2052
(11/19/03 1:20 pm)
 Re: bassman 807's
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 The safest way is to put 1 ohm 1 watt resistors in series with the cathode of each tube.

Measure the voltage drop across the resistors.

A 35mV reading = 35mA of current.

Ken
 
HotBluePlates
I only work on Fender's
Posts: 666
(11/19/03 1:25 pm)
 807 Bassman
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 I'm betting that the distortion you're hearing is normal. If the amp is biased a little hot, I can see a Bassman breaking up at 5.
 
ernie jr
Junior tube assistant
Posts: 26
(11/19/03 1:57 pm)
 bassman bias
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 i plan to bias the o/p tubes tonight. it is on a hoffman board so the 1 ohm resisotrs are already there. i wil set it at 35ma
thanks for all the help. ill post pics when i can
ernie
 
ernie jr
Junior tube assistant
Posts: 36
(11/28/03 5:56 pm)
 setting the bias
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 ok, i tried to set the bias, got one tube at 40ma the other reads about 28. to much mis-match? next step, new tubes?
thanks
ernie
 
Tiny Daddy
I will work on all amps
Posts: 333
(11/28/03 6:28 pm)
 Re: setting the bias
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 They sure dont match! Try some others. And they need to both look the same, such as both RCA with same lettering etc. so they would have been manufactured at about the same time. Otherwise they may not stay matched as they age.
 
ernie jr
Junior tube assistant
Posts: 37
(11/28/03 6:41 pm)
 bias problems
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 they are both rca tubes bought at the same time, (over 30 yrs ago, but stored and hardly ever used)
i have another set, westinghouse, but the tops fell off, so i would have to solder the plate wire on. 807's are cheap. i can get a "matched" pair for about $25
ernie
 
Tiny Daddy
I will work on all amps
Posts: 334
(11/28/03 9:09 pm)
 Re: bias problems
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 Maybe it's not the tubes. Have you swapped the tubes to see if the lower bias current follows the tube, or stays with the socket?
 
Tiny Daddy
I will work on all amps
Posts: 335
(11/28/03 9:12 pm)
 Tops fell off
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 Does anyone know what adhesive is/was used on vacuum tube top caps and bases?
 
bnwitt
Senior tube assistant
Posts: 135
(11/28/03 11:15 pm)
 Re: Tops fell off
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 I thought 807's were 5 pin tetrodes not 8 pin beam power pentodes?
 
ernie jr
Junior tube assistant
Posts: 38
(11/29/03 7:09 am)
 bias probs
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 i will swap the tubes to see if the bias follows the tubes, although i doubt it will, as bias voltage with tubes out is the same at each tube.
807's are 5 pin pentodes. specs are almost the same as 6l6's, but with the plate coming out of the top, they look real retro. plus i have 2 pairs of them with matching o/p trans.
ernie
 
ernie jr
Junior tube assistant
Posts: 66
(2/2/04 9:27 am)
 807 bassman
--------------------------------------------------------------------------------
 ok, finnally got a pair of matched tubes, biased at 40 ma
sounds great. what is the formula for figuring out the o/p of an amp again.
thanks for all the advice
ernie
 
Tiny Daddy
I will work on all amps
Posts: 470
(2/6/04 11:20 am)
 Re: 807 bassman
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 Are you asking how much power your amp will deliver? Depends on how much load (speakers) you connect, and on the size of the output and power transformers and also on the amount of power the output tubes are capable of. 807 power is similar to 6L6GC.
 
ernie jr
Junior tube assistant
Posts: 66
(2/6/04 11:58 am)
 807 bassman
--------------------------------------------------------------------------------
 i thought i had seen a thread that had a formula for figuring out how much each tube was "putting out" based on the b+ volt and the bias? or am i just crazy
thanks
ernie
 
Tiny Daddy
I will work on all amps
Posts: 472
(2/6/04 1:01 pm)
 Re: 807 bassman
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 In general B+ volts and bias current will only tell how much power is being dissipated as waste heat. Unless a particular amp is being discussed, there is no way to know about the power supply and output transformer capabilities.
 
 
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[jhadhar65]

I don't know if anyone watches these EZBoard posts or if ernie jr. is still around, but I sure would like to know how all this eventually worked out for him.

[Geezer]

ernie still stops in to the forum from time to time....I sent him a PM calling his attention to this thread.

Geez'r

[ernie_jr]

the bassman is working well, biased at about 38ma with 450 volts on the plates.
it is a 5f6-a circuit, but with 807's and a 5u4, so it has 3 big coke bottles and
has a nice recto look.. the sound is a bit darker than the sunn 200's and the "sunn/peg" (sunn/ampeg combo amp i built). any other questions, please ask or email me.
ernie

[jhadhar65]

Thanks Geez!

Ernie - I'm really curious about any problems you may have had with plate lead dress and oscillation at any time during or after the build.  Did you take any special precautions with the plate leads?  If so, what were they?  If not, do you have any pictures of your plate lead routing?  I'm seriously leaning toward the 807 or similar for a particular amp design I have and I'm interested in anything unusual you may have run into with yours in any capacity and what your subsequent solutions may have been.

Sorry to be a pain and respond whenever you get around to it... I'll be watching the thread.  Thanks in advance!

Hoyt

[ernie_jr]

did nothing special. in fact, i have it set up so in can run 6l6's or 807's. i set up parallel sockets with the grid stoppers on the octal sockets.. i ran the o/p leads to a tie lug, then ran jumpers to the octal sockets and the plate leads from the 807's
also off the tie lug. plate leads about 8-9 inches long. the amp is dead quiet and
has never had any oscillation problems. i dont have any pics of the amp at this time, sorry. it is mounted on a hammond 10/17 inch chassis with all the tubes
on the back side of the amp. any more questions, please ask.
good luck
ernie

[jhadhar65]

Good information... thanks very much!