Page 1 of 2
loss of volume when linked input
Posted: Wed Aug 25, 2021 3:21 pm
by jujub
Hi to all
It's been a month since got my new 1970 DR103, serial number is 1083. It is original exept for a recap an bias doubler mod.
I come to you because think something is wrong. when I link brilland on the low input and normal channel ther's a significant volume loss. that doesn't happen on my SA212 combo (74')
also alone I find that the brillant channel is less power full thant the normal one.
I've tried to change the preamp and output tube but it didn't changed anything.
Do you have any Idea?
Thanks
Re: loss of volume when linked input
Posted: Thu Aug 26, 2021 11:56 am
by Dr.HI-TONE
post some pics of the input jack assembly and the preamp board associated with V1 and V2.
Re: loss of volume when linked input
Posted: Thu Aug 26, 2021 1:25 pm
by jujub
Here you are sir,
As you can see the 'middle' pot has been changed also 1 tone stack capacitor for bass was return to original mullard at 47n
INPUT JACKS
- 20210826_145932.jpg (510.55 KiB) Viewed 5143 times
- 20210826_150005.jpg (437.06 KiB) Viewed 5143 times
TAG BOARD
- 20210826_150018.jpg (442.26 KiB) Viewed 5143 times
- 20210826_150055.jpg (395.48 KiB) Viewed 5143 times
As you can see this amp is late 1970 (at least october) and so the layout is not the usual one !
Thank you !
Re: loss of volume when linked input
Posted: Thu Aug 26, 2021 1:44 pm
by jujub
I just saw that the middle pot value is wrong...50K instade of 100k...
Re: loss of volume when linked input
Posted: Thu Aug 26, 2021 4:47 pm
by Dr.HI-TONE
That tone stack is not the classic 1971-1974 tone stack. but I don't see a clear problem.
maybe Mark will see something?
Re: loss of volume when linked input
Posted: Fri Aug 27, 2021 5:51 am
by jujub
That's why I was asking...didn't see anything wrong too
Re: loss of volume when linked input
Posted: Fri Aug 27, 2021 12:12 pm
by Dr.HI-TONE
has the bias capacitor been replaced since the pic was taken?
Re: loss of volume when linked input
Posted: Fri Aug 27, 2021 4:59 pm
by mhuss
Does it do this both ways, i.e., jumpering Normal to Brill versus jumpering Brill to Normal?
Re: loss of volume when linked input
Posted: Fri Aug 27, 2021 7:01 pm
by jujub
Yes. no matter how I connect when an input is connected to 'low' ...the output is 'low'.
I should mention that I found brillant Input is 'kind' of weaker than the normal one.
Re: loss of volume when linked input
Posted: Mon Aug 30, 2021 7:37 pm
by mhuss
Did you try replacing V1 (or swapping it with another)?
Re: loss of volume when linked input
Posted: Tue Aug 31, 2021 1:28 am
by jujub
Yes I did. I changed every tubes in there without success
Re: loss of volume when linked input
Posted: Tue Aug 31, 2021 7:41 pm
by mhuss
I'm not sure how you're jumpering, but if you go into the low gain input and jumper that high into the other low gain input, you're going to have a pretty weak signal. The optimal way is to go into the high gain input and jumper that Low to the other channel high.
Re: loss of volume when linked input
Posted: Tue Aug 31, 2021 8:10 pm
by jujub
Here's what I do... as for the others Hiwatt I got
- 20210831_215657.jpg (154.83 KiB) Viewed 5093 times
Re: loss of volume when linked input
Posted: Wed Sep 01, 2021 9:51 pm
by mhuss
That looks fine. The only other thing I can think of is to test the values of the 220k resistors and 22n & 1n caps shown in your first pic above, and if they're OK, check the 2k2 cathode resistors and cap.
Re: loss of volume when linked input
Posted: Fri Sep 03, 2021 2:01 pm
by jujub
That big boy gone up to 250nF
- Capture.PNG (17.82 KiB) Viewed 5057 times
- Capture2.PNG (310.39 KiB) Viewed 5057 times